Fixed assert error with zsh

with my zsh config I got the following error when I opened a new tab
Gdk-CRITICAL **: IA__gdk_window_set_title: assertion `title != NULL' failed

I added a check for NULL.
Merge https://github.com/caleb-/evilvte
Added missing linker option for intl

Since FreeBSD-10 clang is the standard compiler and clang seems to need
the gettext library explicitly added in the options.
Merge pull request #27 from tantSinnister/master

Compiling evilvte with clang on FreeBSD