For the directory install, if the path is relative and the extension expects to run configure, the path to configure is bogus as the subprocess runs the extension directory. For the file install, if the extension expects to run configure before make, Makefile does not necessarily exit, so discerning the extension's directory by any of 'Makefile', 'makefile' or 'GNUMakefile' was not enough.
Fix issue #10
Include the command in the error message.
Fix issue #11.
Fixes ticket #7