mapscript segfault when creating an unupported output format

[unicoletti]

I have accidentally compile mapserver 4.4.0 without pdf support and then tried
to produce pdf output from Java mapscript.
The result is that the JVM crashes because of a segfault in native code. The
error is in the constructor of outputFormatObj which should be modified to
handle this situation more gracefully by launching an exception.

I attach a patch that fixes the problem.

[unicoletti]

The constructor throws an exception when an unsopported outputFormat is requested

[sgillies@…]

Thanks for pointing this out, Umberto.  Fixed.  Ideally, the errors should be set
in mapoutput.c, but for now this will do.  I wrote a new unit test so that we will
be able to look out for this in the future.

Committed to branch-4-4 and CVS HEAD.