lib-mail: Moved message_skip_virtual() to message-size.[ch] and changed API

Marked functions parameters that are allowed to be NULL. Some APIs were also changed. The non-obvious APIs where NULL parameter was changed to "" are master_service_init() and auth_master_user_list_init(). These checks can currently be enabled only on a patched clang: http://llvm.org/bugs/show_bug.cgi?id=6786

Message parsing/reading: If read returns failure, don't ignore the error. --HG-- branch : HEAD

Changed .h ifdef/defines to use <NAME>_H format. --HG-- branch : HEAD

Added "bool" type and changed all ints that were used as booleans to bool. --HG-- branch : HEAD

Removed useless parameters from message_get_body_size(). Also did some small optimizations to it. --HG-- branch : HEAD

IMAP protocol doesn't allow server to send NULs to client. Send ascii #128 instead. --HG-- branch : HEAD

Partial fetches were broken when they stopped between virtual CR and LF. --HG-- branch : HEAD

mail-storage.h interface changes, affects pretty much everything. FETCH, SEARCH, SORT and THREAD handling were pretty much moved from lib-storage/ to imap/ so adding non-index storages would be much easier now. Also POP3 server can now be easily implemented with lib-storage. Not too well tested, and at least one major problem: partial fetching is _slow_. --HG-- branch : HEAD

Naming style changes, finally got tired of most of the typedefs. Also the previous enum -> macro change reverted so that we don't use the highest bit anymore, that's incompatible with old indexes so they will be rebuilt. --HG-- branch : HEAD

Some bugfixes and speedups for partial fetch handling. --HG-- branch : HEAD

Marked all non-trivial buffer modifications with @UNSAFE tag. Several cleanups and a couple of minor bugfixes. --HG-- branch : HEAD

Renamed IBuffer and OBuffer to IStream and OStream which describes their functionality better. I tried to keep the variable names and comments also sensible. --HG-- branch : HEAD

Split IOBuffer into mmaped IBuffer, file IBuffer, memory data IBuffer and file OBuffer. --HG-- branch : HEAD

Introduced uoff_t which is the unsigned-equilevant of off_t. This was needed to be able to handle off_t overflows properly. Also changed a few unsigned int fields into uoff_t so we should now support >2G mails if uoff_t is 64bit. Also fixed several potential integer overflows. --HG-- branch : HEAD

Message data is parsed in blocks (no longer entirely mmap()ed). Several IOBuffer changes. All mixed signed/unsigned comparisions were fixed so code can now be compiled with gcc's -W flag. mbox support is broken currently, and there's most likely several other problems too. --HG-- branch : HEAD

Initial revision --HG-- branch : HEAD