mod_lua: Also check for 5.2 headers/libraries, we support both 5.1 and 5.2 nowadays.

Follow-up to r1488773 for configure builds.

Add database features for mod_lua (apr_dbd + mod_dbd). See documentation update for API and examples.

configure: Fix processing of --disable-FEATURE for various features.

Spin off module-specific build options into separate build vars. [second try, supersedes r1385214] Add MOD_CFLAGS, MOD_LDFLAGS variables etc. to the build commands, which are available to modules for customization on a per-subdir basis (by adding definitions to modules.mk). Reduces the risk of side-effects when a module needs to add CFLAGS, LDFLAGS etc. and these would be added to the global settings (ALL_CFLAGS etc.). Adapt build settings for mod_ssl, mod_socache_dc, mod_deflate, mod_xml2enc, mod_proxy_html, and mod_lua to use the new MOD_xxx build variables. Change PICFLAGS, SHLTCFLAGS and LTCFLAGS into config vars, instead of AC_SUBSTing them in build/rules.mk.in. For support/ab, introduce ab_CFLAGS and ab_LDFLAGS, and define explicit make targets where they appear at the proper position in the build commands. Consistently use "--with-xxx=PATH" in configure help strings which are used to specify a path to the installation directory of an auxiliary package.

revert r1385214, as I inadvertently left out acinclude.m4.

Spin off module-specific build options into separate build vars. Add MOD_CFLAGS, MOD_LDFLAGS variables etc. to the build commands, which are available to modules for customization on a per-subdir basis (by adding definitions to modules.mk). Reduces the risk of side-effects when a module needs to add CFLAGS, LDFLAGS etc. and these would be added to the global settings (ALL_CFLAGS etc.). Adapt build settings for mod_ssl, mod_socache_dc, mod_deflate, mod_xml2enc, mod_proxy_html, and mod_lua to use the new MOD_xxx build variables. Change PICFLAGS, SHLTCFLAGS and LTCFLAGS into config vars, instead of AC_SUBSTing them in build/rules.mk.in. For support/ab, introduce ab_CFLAGS and ab_LDFLAGS, and define explicit make targets where they appear at the proper position in the build commands. Consistently use "--with-xxx=PATH" in configure help strings which are used to specify a path to the installation directory of an auxiliary package.

enable mod_lua at level 'all' if the dependencies are present

Allow to specify module specific custom linker flags via the MOD_XXX_LDADD variables. Use APR_ADDTO instead of APR_SETVAR or direct variable assignment. This is especially useful when building mod_lua or mod_deflate against a lua resp. libz which are installed in non-standard locations. One can add "-R ..." to MOD_LUA_LDADD and MOD_DEFLATE_LDADD before configure to fix the RPATH/RUNPATH of those modules.

Tolerate dependency checking failures in configure for modules that have been enabled only implicitely.

Respect platform specific runpath linker flag when building mod_deflate and mod_lua.

Fix configure error when configuring module set "reallyall".

Use "=" instead of "==" in test condition for improved shell compatibility.

Always make mod_*.h files available where they exist, modpath by modpath

Add . 'default' test first before searching paths, to determine if the lua.h, liblua5.1, liblua-5.1 or liblua can be resolved. This avoids adding strange paths on fedora/redhat, and choosing the wrong /lib[64] flavor. Also ensure -lm is always added to the actual linked libraries, avoiding a LoadModule failure on fedora/redhat. Still should first try to search for pkg-config lua settings, but note this would break fedora until that build hackery is corrected, c.f. the bug https://bugzilla.redhat.com/show_bug.cgi?id=499238

Use LDADD mechanism to only link mod_serf resp. mod_lua to libserf resp. liblua. No need to include this dependency in all other modules and binaries.

Use APACHE_HELP_STRING() for --enable-luajit in configure to allow automatic indentation in configure help output.

Hack to add basic support for LuaJIT.

Rename all files in mod_lua to have a lua_ prefix, as things like 'config.h' are way to generic and will often conflict with other include files.

Rename mod_wombat -> mod_lua. Note that this isn't a complete transformation yet, but it should basically compile and load as mod_lua.