Fix attempting to toggle visibility when tray disabled
Take two at fixing out of source builds
travis: Add clang & CPUs & fast_finish

HexChat seems to compile fine with clang so why to not test it too.
-j$(nproc) seems to work with HexChat and fast-finish marks build as
failed if one job fails.

Fast finish won't stop jobs that aren't finished at the time of failure.

Closes #1147
Fixed instances of hexchat_printf that unsafely used a string parameter as a format string.

Fixes #1153
Fix parsing of MONITOR responses

Fixes #1157
Merge branch 'master' of https://github.com/hexchat/hexchat