Update LibSoup version for new WebKit and fix build.

Includes:
* Providing for downloading prebuilt Libsoup instead of building
* Patches for Libsoup bugs
* adjusting the SQLITE_CFLAGS and SQLITE_LIBS to match what LibSoup's
configure looks for.
* Second WebKit patch and some comments about what's needed to build it.
Install GnuTLS from prebuilt tarballs, optionally build from source.

NB: Building from source requires manual intervention as libgpg-error's
ro.po requires conversion from ISO8859-2 to UTF8, which causes a hang.
Fix hang when building libgpg-error.
Build glib-networking (required by libsoup) in gnutls.

Ensure that its version is coordinated with glib's by using new variable
GLIB_VERSION for both.
Fix up libgnutls installation when building from source.

We don't actually build libgnutls from source, so we need to create the
directory for it. The .la files it provides contain the builder's paths
which screws up libtool later, so delete them.
Get rid of some of the libfoo.la has moved warnings.

The warning is caused by finding the libtool-lib on a different path than
the one encoded in its libdir statement; it's a purely lexical check,
so if the mingw version, /c/gcdev is given in the -L directive and c:/gcdev
is in the libdir statement, libtool will issue the warning.

The only one remaining is libintl, which is usually found with /c/gcdev/mingw/lib
but whose libdir=/mingw.
Unfortunately just about every other library links to this so it's issued
a lot.
Rewrite libtool link files (libfoo.la) for certain cached-build directories.

To always point to the current installation directory.

* Ensures that build targets linking those files always have a valid and
correct path.
* Reduces the number of "appears to have moved" warnings.
Rewrite /c/gcdev/ to $GLOBAL_DIR in targeted libtool archives.

* Ensures all directly-linked libtool archives in "dependency_libs" are
linked from the right directory
* Reduces the number of "appears to have been moved" warnings.
Add libtiff and libjpeg to the collection of precompiled packages

We were using precompiled packages of these before from the Gnome binary
collection, but that libtiff had an obsolete link request to
libjpeg-uchar-boolean-8.dll. These editions are compiled from the latest
sources and should avoid the bad rpath.
Switch sed for perl in libtool-archive cleanup.
Update guile load path after guile modules were moved in the gnucash source tree