Workaround for audio meter widget getting stuck
Merge pull request #195 from hwdro/master

Workaround for audio meter widget getting stuck.
Set minimum version on mac to 10.8.5
Add dstr_end function to get the last character
Fix dstr_end bug (it's len - 1)

Somewhat of an embarassing fix.  Using 'len' will just return the null
terminator.
Prevent loading image files with null/empty paths
Fix NULL pointer dereference with text lookups
Add IObsPlugin interfaces for Video Source Plugins
Make XComposite capture use new C++ plugin helper