Bump libcamel soname for some upcoming API changes.
Remove camel_tolower().

Use g_ascii_tolower() instead.
Remove camel_toupper().

Use g_ascii_toupper() instead.
Remove camel_string_list_free().

Use g_list_free_full(list, (GDestroyNotify) g_free) instead.
Remove "camel_store_summary_info_free" backward-compat macro.

This macro was temporary... very temporary.
Remove unused CAMEL_MESSAGE_USER_NOT_DELETABLE flag.
Remove unused CAMEL_MESSAGE_HIDDEN flag.
Remove unused camel_imapx_summary_add_offline().
Remove unused camel_imapx_summary_add_offline_uncached().
CamelVeeMessageInfo: Remove unused 'old_flags' member.

Set in various places but never used.
CamelStoreSummary: Move 'store_info_size' to class struct.

Allocation size varies by CamelStoreSummary subclass, not by instance.
CamelFolderSummary cleanups.
CamelFolderSummary: Remove unused migration gunk.
Remove camel_folder_summary_add_from_header().

Trivial function, not worth the API bloat.  Do this instead:

  info = camel_folder_summary_info_new_from_header (summary, headers);
  camel_folder_summary_add (summary, info);
Remove camel_folder_summary_add_from_parser().

Trivial function, not worth the API bloat.  Do this instead:

  info = camel_folder_summary_info_new_from_parser (summary, parser);
  camel_folder_summary_add (summary, info);
Remove camel_folder_summary_add_from_message().

Trivial function, not worth the API bloat.  Do this instead:

  info = camel_folder_summary_info_new_from_message (summary, message, NULL);
  camel_folder_summary_add (summary, info);
CamelMessageInfo: Use atomic operations to track reference count.
Remove CAMEL_FOLDER_SUMMARY_REF_LOCK.

No longer used, reference counting operations are now atomic.
Remove CAMEL_FOLDER_SUMMARY_IO_LOCK.

Not even the private 'io_lock' mutex was used.
Remove CAMEL_FOLDER_SUMMARY_FILTER_LOCK.

This is a private mutex, don't expose it in the public API.