saves a bit of typing and not necessary if you look at how it is used.
Conflicts:
gtk2_ardour/about.cc
gtk2_ardour/session_dialog.cc
libs/pbd/system_exec.cc
When creating a SystemExec from a command-line, search $PATH for the
command to execute, so that post-export hooks don't need to specify a full
path.
Conflicts:
libs/pbd/system_exec.cc
Make sure to copy any part of the command line after the last delimiter
to argv[] when creating a SystemExec with an escaped command line.
Conflicts:
libs/pbd/system_exec.cc
