Add support for a Payment Protocol to Bitcoin-Qt.

Payment messages are protocol-buffer encoded and communicated over
http(s), so this adds a dependency on the Google protocol buffer
library, and requires Qt with OpenSSL support.

Two changes: make some linux-specific linker options linux and linker specific.
And in the cross-compile environment, prefer the $HOME/qt/bin tools to
whatever might be somewhere else in the path.

Fixes issue#2288. Includes cleanups from Luke's pull 2243.

Bump deps tp 0.0.5
Small docs corrections

Keeps the "windows", "windowsxp", "windowsvista" styles.

Reduces the size of a static bitcoin-qt.exe by ~400 kB.

Replace all occurances of license.txt with COPYING, including naming the file COPYING.txt on Windows

All client version information is moved to version.cpp, which optionally
(-DHAVE_BUILD_INFO) includes build.h. build.h is automatically generated
on supporting platforms via contrib/genbuild.sh, using git describe.

The git export-subst attribute is used to put the commit id statically
in version.cpp inside generated archives, and this value is used if no
build.h is present.

The gitian descriptors are modified to use git archive instead of a
copy, to create the src/ directory in the output. This way,
src/src/version.cpp will contain the static commit id. To prevent
gitian builds from getting the "-dirty" marker in their git-describe
generated identifiers, no touching of files or running sed on the
makefile is performed anymore. This does not seem to influence
determinism.

Thanks to makomk for finding the bugs here and devrandom
for passing them along (see
https://bitcointalk.org/index.php?topic=42198.msg514312#msg514312)

* Upgrade to use miniupnpc 1.6
* Upgrade to wxWidgets 2.9.2
* Upgrade to Bost 1.47 for Win32 Builds

Also fix a minor type in gitian.yml

This adds the relevent patches which are applied to wx,
and updates for cross compiling.