Fix problem configuring path not containing spaces.

This change forces `compilation-start` to cd to default-directory by inserting dummy cd at front of the command.  Without this, the old broken version of compilation-start (see http://debbugs.gnu.org/cgi/bugreport.cgi?bug=12640) may pick up quoted path without spaces and then assume the quotes are part of the path.  This causes the error in #1.

Closes #1.