Introduce a function to determine if a function was disabled in the PHP config
Check if exec is available before using it

This avoids fatal errors if the function has been disabled.
It is only used in this function.
Add unit tests for hmbkp_is_function_available

These unit tests use custom php ini configs
Unit tests php ini configs
Return true on success, false on failure
Fix group flags
Filter tests to run

Some tests require custom php.ini configs
Rename function
Update tests to reflect function name change
Update command to reflect function rename
Regenerate github account info
we do this in travis.yml
Use $TRAVIS_BUILD_DIR
Display placeholder if exec fails
Remove hard line returns
Merge branch 'master' into issue-620
Use HM_Backup function to determine if shell_exec is enabled
Fix deleted function
Merge pull request #620 from humanmade/issue-620

Several reports of issues with 3.0.2