Support parameter "gnuConfigurePrepareSkip".

Some source tree uses symbolic link.
But previous versions of Java doesn't API to create symlinks.
So it may causes strange behavior on the build stage. (refs #82)

GNU configure can build binaries on the different place from its source directory.
[like: "mkdir bin; cd bin; ../src/configure" ]
So in some cases, we don't need to copy.
But some source tree may have no configure but configure.ac.
In such cases, we should copy sources into target/gnu/** .

This patch provides parameter named "gnuConfigurePrepareSkip".
It has boolean value.
True means "not copy sources, not run autogen/buildconf."
The default is false. So it keeps the backward compatiblity.

gnuConfigurePrepareSkip has a good side-effect.
You can reduce your disk usage.
It may be remarkable if you build huge system like GCC.