Fix HTTP leading to "Invalid File" error

The =~ operator returns an integer that tells you where in the input the pattern was found. You should NOT convert this into an integer because an index of 0 would become false.
Let operating system find mplayer

This will find mplayer no matter where it is as long as the directory in PATH (which it is for most installations)
Fix URI::regexp check in SlaveCommands
Quote filename for load_file and load_list commands
Update tests
Update tests
Merge remote-tracking branch 'origin/patch-1'
Merge remote-tracking branch 'origin/patch-2'
Merge remote-tracking branch 'origin/patch-3'