This essentially reverts 1bf8eef14f
which tried to prefer file procedured that are GIO-enabled over
indirect loading via the file-uri plug-in. But file-uri is gone now so
we can treat all file procedured the same again, restoring the
original logic.
Now a file procedure which specifies only an extension is again
preferred over magic matching.
Change file magic matching from using a simple boolean "magic matches"
logic to using a matching quality. The quality is measured by the
number of bytes that matched.
Matching a single file procedure's magics now tries all magics and
returns the best match quality.
Searching a file procedure for a given file now tries all file
procedures and returns the one with the best match quality.
This fixes raw camera files being opened as TIFF, given a better magic
than just the generic TIFF magic is provided.
file-procedure.[ch] is gone and its functions moved to
GimpPlugInManager where they belong (the manager keeps around the
lists of load, save and export procedures).
Utility functions from file-utils.[ch] that have nothing to do with
image files moved to core/gimp-utils.[ch].
