Corrected a crashing bug in mail threading.
Added mail_rebuild script, which rebuilds the indexes.
Wider filename field in mail import form.
Don't allow ? characters in URLs.
Imported around 1,500 mail messages successfully to test.
Changed the build system to use ocamldsort to produce the correct
build order. Moved the library code into lib/ so that it is
conveniently separate from the script code. Scripts and library
modules no longer need to be listed in the Makefile.
Debian: Build-depends on ocamldsort.