With this commit, errors and warnings can use message box even before LyX is properly...

With this commit, errors and warnings can use message box even before LyX is properly initialized. This is especially useful for missing sysdir and/or userdir directory.

* Alert.C:
  - error(): calls error_pimpl() in any case.
  - warning(): calls warning_pimpl() in any case.

* Alert_pimpl.C:
  - error_pimpl(): construct a QApplication if LyX is not initialized yet.
  - warning_pimpl(): ditto.

* lyx_main.C:
  - parse_sysdir(): replace lyxerr with Alert::error().
  - parse_userdir(): ditto.

git-svn-id: svn://svn.lyx.org/lyx/lyx-devel/trunk@16823 a592a061-630c-0410-9148-cb99ea01b6c8