lib-storage: index: Made MIME FILENAME search criterion match case-insensitively.

Partially implemented IMAP SEARCH=X-MIMEPART capability. This capability is currently Dovecot-specific.

global: unsigned int:1 -> bool:1 perl -i -pe 's/unsigned int ([^,:;]+):1;/bool $1:1;/' **/*.[ch]

Array API changed: ARRAY_DEFINE(name, type) -> ARRAY(type) name Easy way to update your existing code: perl -i -pe 's:ARRAY_DEFINE\(([^,]+), *([^)]+)\);:ARRAY($2) $1;:' **/*.[ch]

lib-storage: Fixed searching message flags with private flags index.

Fix the build failure on AIX

Search supports now prefetching data for returned mails. Dropped imapc's own prefetching. mail_prefetch_count specifies how many mails can be kept open and issue a prefetch. This works using posix_fadvise(POSIX_FADV_WILLNEED) for maildir, sdbox and cydir backends. Apparently only Linux supports this. imapc backend also implements this internally by sending wanted IMAP commands to remote server. The command pipelining helps with latency. This change also makes it actually possible for imapc backend to first check if wanted data is already cached in local index and avoid sending unnecessary IMAP commands to remote server.

Changed header/body searching to do search key charset translation earlier. This cleans up and simplifies error handling.

lib-storage: Changed mailbox_search_*() API to return pointer struct mail. This reduces the flexibility, because now different mailbox_search_next() calls can't have different mail parameters with possibly different wanted_fields settings. This flexibility was never used though, and removing it gives a couple of benefits: * it's now easier for backends to implement prefetch and parallel search * usage is easier since mail_alloc()/mail_free() is no longer needed

lib-storage: Moved setting "wanted fields/headers" fields for sort program from imap-specific code. Also separate between fields that are actually wanted to be fetched from the fields that sorting wants to temporarily use.

lib-storage: Index search context is now more accessible by backends. Moved struct index_search_context to index-search-private.h and added recheck_index_args flag that backends can set.