enabled moving of virtual folders.
update summary caches on receiving.
fixed virtual class structure.
exclude trash on recursive search.
fixed renaming of virtual folders.
implemented the modification of search folder condition.
fixes a bug that search cache occasionally didn't work.
fixed a bug that search folders under IMAP4 or NNTP folders couldn't be removed.
cache search result to speed up on and after the second search.
some modification of searching.
implemented query search and virtual folder (merged from newsearch branch).