fts-solr: Fixed HTTPS support by properly propagating SSL client settings from mail_user.

fts-solr: Use built-in lib-http instead of libcurl. Removed libcurl dependency.

fts-solr-old: Mailbox names are mUTF-7 in the Solr index, not UTF-8.

fts: Redesigned/enhanced FTS API and how virtual plugin works with it. The changes include: - Only indexer process and "doveadm index" do FTS indexing now. Other processes connect to the indexer process via UNIX socket and request indexing a specific mailbox. - FTS backends can now index/search any search key. Current backends implement indexing for some specific header fields (Subject, From, To, Cc, Bcc), but it would also be possible to add indexing for e.g. message size or date. - CLucene support is fixed and fully functional. - Solr is split to "solr" and "solr_old" backends. The new "solr" backend supports the new header fields. It also uses mailbox GUIDs as mailbox identifiers, so that renaming a mailbox doesn't require reindexing. The "solr_old" uses the old Solr schema and doesn't support any new features.

Use -Wl,--as-needed -Wl,--no-undefined GNU ld flags for non-plugins.

Added dovecot.m4 file that external plugins can use. Based on patch by Dennis Schridde. --HG-- branch : HEAD

OSX: Don't try add plugin dependencies. It just breaks plugin loading. --HG-- branch : HEAD

plugins: Added dependencies. The dependencies can only be checked if the dlopen() can successfully open the module, so use (apparently) non-portable ltlibrary linking to force the libraries we depend on to load with us. --HG-- branch : HEAD

Get rid of imap/, pop3/, lda/ and sql/ module subdirs. It's all in lib/dovecot/ now. --HG-- branch : HEAD

Symlink FTS plugins to pop3 directory too. --HG-- branch : HEAD

solr-schema.xml move was forgotten from Makefiles. --HG-- branch : HEAD

fts-solr: Compiling fixes. --HG-- branch : HEAD

Initial code to support Apache Solr (Lucene indexing server). --HG-- branch : HEAD