plug-ins: 64bit double saving support for file-fits

Quickly hacked up, loads again using the plug-in.
modules: plug leak in color-selector-cmyk

Don't leak the RGB profile if the CMYK profile can't be loaded
libgimpwidgets: don't leak the empty_iter in GimpIntStore
libgimpmodule: disconnect from the modules' "modified" signal

when GimpModuleDB is finalized.
libgimpconfig: don't leak "expanded" in gimp_config_path_expand_to_files()
app: don't leak the gimpdir GFile in app_run()
app: don't leak all results from separate_uline_pattern() in GimpSpinScale
app: don't leak "buffer" in gimp_interpreter_db_add_binfmt_misc()
app: free the default brush, pattern etc in gimp_finalize()

and print a warning if there are any contexts left in gimp->context_list.
Bug 738037 - Wrong order of parameters in the Sobel plugin

Get the parameters from the right PDB arguments (parameter index was
off-by-one).
app: don't leak "display_file" in gimp_image_format_display_uri()
app: don't leak the GFileInfo in file_open_image() and file_save()
app: remove unclear fix from gimp_tool_options_editor_tool_changed()

It was introduced in e7ade3f8eca30edb63db4dde075540a3676aea67. The
g_return_if_fail() is IMO useless, the actual fix (which I kept) was
pulling the call to gimp_tool_options_editor_presets_update() inside
the if().
app: don't ref the tool options GUI in gimp_tool_options_editor_dispose()

They are kept alive by a ref owned by GimpToolOptions, refing them
here made them all being leaked on exit.
plug-ins, PDB: remove edge-sobel and add a PDB compat procedure
app: add gegl:oilify to Filters -> Artistic
app: move all GimpBrush members to a private struct

Add and use accessors for width, height, x_axis and y_axis.
Bug 730211 - Extra zeroes appear in XCF files

Don't use xcf_seek_end() because that seems to be broken on certain
file systems / operating systems / FUSE mounts / whatever. Instead,
seek to explicitly calculated file offsets.

Ported Massimo's patch to master and added comments --Mitch

The same commit in gimp-2-8 is a57e49b1bbd318b06c4f8d578557b63256a1e66d
app: remove xcf_seek_end(), it's unused, and should not be used any longer
app: use xcf_write_int32_check_error() for all XCF property writing

Some (copy/paste I guess) places used xcf_write_int32() plus manual
error checking for no reason.