Add devrc.sh which makes it easy to set the environment for hand-building
Register some environment variables.

These variables weren't added to the register list when they were added
to install-impl.sh.
Update WebKitGtk to a new one built with the current MinGW toolchain.

Provide new patch, URLs, dependencies, etc.
Restore libgcrypt to gnutls; included in older binary, not in new one.
Must make the webkit dir before unpacking into it.