more configure-time support for dynamically loadable MPMs: . axe --with-mpm="shared" hack, replace with --enable-mpms-shared={all|list} . replace singular MPM_NAME with access to the list of enabled MPMs . replace singular MPM_SUBDIR with list MPM_SUBDIRS . enable OS/2 MPM in same manner as others with configure support instead of hard-coding in configure.in Current state: MPMs are built as static archives (but not linked to httpd) with --enable-mpms-shared, so they still have to be built with apxs to load dynamically.

Added support for MPMs that live in subdirectories under server/mpm like server/mpm/experimental/*

rules.mk is stored in $(top_blddir). Without this change, VPATH builds stop working.

Overall UNIX build system improvements: * Makefile header is now completely dynamic * Absolute paths everywhere (fixes Tru64 support) * Get rid of LTLIBRARY_SHARED_NAME rule in library.mk (fixes Irix support, untested) * VPATH does not contain variables anymore (fixes UnixWare support) * Remove inclusion of program.mk in support/Makefile.in (PROGRAM_NAME is empty => breaks Irix and others) * Call REENTRANCY_FLAGS earlier, so that flags are passed to header checks (might fix OpenBSD pthread.h-detection, untested)

Minor nit: use top_srcdir instead of topsrcdir, to be more consistent with autoconf.

These changes are committed together, because they depend on each other. - shared modules can be built in the tree - added support for --with-layout, uses APACI's config.layout - working 'make install' - working 'make depend' - working Pthreads checks - buildconf replaced