* filter-xml.[ch]: add a "string" type
* filtertype.xml, vfoldertypes.xml: Use type="string" rather than
"folder" for subject/body matching.
* filter-arg-types.c: Update some strings for "text" input. Fix
some warnings (including one that pointed out a real bug).
* filter-arg.c, filter-druid.c, filter-format.c: fix warnings
svn path=/trunk/; revision=4025