Add gawk package for x86, x86_64 and x86_gcc2.
ScreenSaver: pass in true to get a preview

Fixes #10602

This was a simple mistake on my part, unfortunately this means that
a bunch of screen savers that showed preview fine before no longer do.
gawk: use the HaikuPorts package.

* left the in-tree version as its libintl is used by gdb.
* added as bootstrap package.
PackageInstaller: Unbreak selecting custom install folders.

BFilePanel always sends B_CANCEL when it hides (as documented in the BeBook),
not just when the user cancels the file panel. Track what message we expect
and only react to B_CANCEL when it means the user really canceled selecting
the target folder.