SVN_SILENT made messages (.desktop file)
support explicit and automatic draft storage
qt5 build fixes
IMAP: don't error out on "-2" being passed as an unsigned int

This has been reported by a user of seznam.cz. It's obviously a server error,
but we don't have the luxury of being able to just point at their bugs.
tests: enable an old test case which was commented out

Now that we have tests which don't actually require the full-blown expected
output to be constructed, let's use them for these old relics as well.