[Bug-gnubg] First GTK 2.4 File Requesters working

[macherius]

Finally I have visible results, all file requesters of type FDT_NONE are
convertet into stylish  GTK 2.4 FileChoosers, including some basic path and
filter magic. Yes, that's 2.4 and not 2.6, so the majority of the penguin
fraction will also get the benefit. As in the new GTK there is a difference
between open and save dialogs, the type was split into two. 

Now I'm unsure how to proceed. Should I submit several small patches (to
Jon?), or come up with a monster? Personally I prefer the step by step
method, in particular as what is there is already a user visible improvement
for the upcoming premiere of GTK 2.6. Because whatever comes next requires
harder cuts, so far i just decorated functions. Any step further requires
new data structures, and that may leave the code in flame for a while.

Please advise,
Ingo

P.S. Preview patch on request and public demand.