Major overhaul of rootmenu's file handling.

Major overhaul of rootmenu's file handling.

This diff fixes a huge amount of issues that could be triggered by using
the old-fashioned configuration files, i.e menu.  They can be activated
by using a line like "/path/to/menu".  On most systems, this file will be
parsed with cpp and the result sent through a pipe to WindowMaker.

Anyway, in the code path, memory leaks and buffer overruns await. I have
tried to fix these parts, but in the end it is more or less a rewrite,
whereas I used WINGs whenever possible.

Difference to previous implementation, beside of bugfixes:
- You are free to use single quotes and double quotes in configuration
- Linewrapping is allowed for other pipe'd data, too
- In general, line reading is unified throughout that file

Bugfixes:
- Avoid buffer overrun on lines which have line wrappings, that will happen
  ALWAYS, because wtrimspace-usage was erroneously.
- Avoid memory leak, also happened through wtrimspace usage.
- Avoid buffer overrun in separateline if a line ending happens early.
- Actually handle ferror() instead of only feof(), that would result in
  endless spinning
- A line wrapping at the end of a file is an error.