use command substitution for fc correction check
Fix pipe/&& precedence for some bash versions

Per @martinlauer, PR#11
The check didn't work in bash v4.3.11(linux) or bash v4.3.25(osx).
Using Bash 3.2 or Zsh 5.0.6 everything worked fine.

Fix via @nilbus, the above syntax works correctly to execute the
appropriate logic.
Merge branch 'martinlauer-master' into testing