allow more liberal version regexp in EnvironmentModulesC

Older versions of environment modules (C) simply output version strings like `3.1.6`.  Make the VERSION_REGEXP accept this.
Merge branch 'develop' into flexible_modulecmd_version
fix incorrect '^' in modulecmd version regexp
Merge pull request #930 from boegel/flexible_modulecmd_version

make 'VERSION=' part in modulecmd version regex optional