Remove the file-path utilities from qofsession.c and move them into a

[Linas Vepstas]

Log Message:
-----------
Remove the file-path utilities from qofsession.c and move them into
a temp file 'gnc-filepath-utils.c' which is used by both the 
file backend and by the app-file GUI routines.  Some of the file-resolution
logic was oved to the file backend.

Modified Files:
--------------
    gnucash/src/app-file:
        gnc-file.c
    gnucash/src/backend/file:
        gnc-backend-file.c
        gnc-backend-file.h
    gnucash/src/engine:
        Makefile.am
        gw-engine-spec.scm
        qofbackend-p.h
        qofbackend.c
        qofsession-p.h
        qofsession.c
        qofsession.h
    gnucash/src/engine/test:
        test-resolve-file-path.c