Please describe the problem:
With 2.15.1, modules/sftp-method.c uses __FUNCTION__ in a number of debug
messages.  __FUNCTION__ is a gcc-ism; C9X provides __func__ and glib provides a
portable define G_GNUC_FUNCTION.

Since sftp-method.c is already including the necessary glib header files, it's
trivial to change all the __FUNCTION__ instances to G_GNUC_FUNCTION.

Steps to reproduce:
Build gnome-vfs-2.15.1 with a compiler other than gcc.

Actual results:
Compile failure in sftp-method.c:

 cc -DHAVE_CONFIG_H -I. -I. -I.. -I.. -I.. -I../imported/neon -mt -DORBIT2=1
-I/local/gnu/include/glib-2.0 -I/local/gnu/lib/64/glib-2.0/include
-I/local/gnu/include/libxml2 -I/local/gnu/include/gconf/2
-I/local/gnu/include/orbit-2.0 -mt -DORBIT2=1 -I/local/gnu/include/glib-2.0
-I/local/gnu/lib/64/glib-2.0/include -I/local/gnu/include/gconf/2
-I/local/gnu/include/orbit-2.0 -I/local/krb5/include -D_FILE_OFFSET_BITS=64
-D_BSD_SOURCE -D_LARGEFILE64_SOURCE -D_POSIX_PTHREAD_SEMANTICS -D_REENTRANT
-DSSH_PROGRAM=\"/local/bin/ssh\" -DG_DISABLE_DEPRECATED
-DGNOME_VFS_PREFIX=\"/local/gnu\" -DGNOME_VFS_DATADIR=\"/local/gnu/share\"
-DGNOME_VFS_LIBDIR=\"/local/gnu/lib/64\"
-DGNOME_VFS_SYSCONFDIR=\"/etc/local/gnu\" -DG_LOG_DOMAIN=\"gnome-vfs-modules\"
-I/local/include -I/local/gnu/include -I/local/openssl/include -I/local/include
-I/local/gnu/include -I/local/openssl/include -Xa -xO2 -xstrconst -mt -KPIC
-xtarget=native -xarch=amd64 -c sftp-method.c  -KPIC -DPIC -o .libs/sftp-method.o
"sftp-method.c", line 2392: undefined symbol: __FUNCTION__
cc: acomp failed for sftp-method.c


Expected results:
Source file compiles

Does this happen every time?
Yes

Other information:
The trivial patch is attached