Multiple memory leaks fixed, and cache trash avoiding

[Philip Van Hoof <spam pvanhoof be>]

I fixed multiple leaks and reintroduced the hashtable of the summary
under a conditional situation.

In case camel_folder_summary_prepare_hash (s) happened, the hashtable
will be used until .. camel_folder_summary_kill_hash (s) happened.

I added these methods to the most relevant locations all over
camel-lite.

For example when saving (unmapping, dumping the summary to the
filesystem and reloading or remapping everything), the hashtable is used
because I know that this is a spot where a lot lookups by uid are going
to be needed.

All the by-uid lookup functions will also detect whether there's a
hashtable available or not, of course.

I guess this is the perfect tradeoff between not wanting to use too much
memory, yet not constantly trashing your cache either. Unless somebody
has a better idea?



-- 
Philip Van Hoof, software developer
home: me at pvanhoof dot be 
gnome: pvanhoof at gnome dot org 
http://www.pvanhoof.be/blog