Add RPM Spec syntax checker [#480]
Remove --info from rpmlint checker

We don't parse the info messages anyway, so there's no use in emitting
them.
Simplify line number correction of rpmlint
Install rpmlint in the testing environments
Improve the rpmlint test case

Include an error, and messages with line numbers
Support RPM Spec Mode in rpm-rpmlint
[Fix #481] Merge branch 'rpmlint'

* rpmlint:
  Support RPM Spec Mode in rpm-rpmlint
  Improve the rpmlint test case
  Install rpmlint in the testing environments
  Simplify line number correction of rpmlint
  Remove --info from rpmlint checker
  Add RPM Spec syntax checker [#480]
Update changelog, credits and texinfo manual [#481]