Update BUILDING.md

Added libminiupnpc-dev package for Ubuntu dependency list.
Little fixes found using clang on OSX10.9:
* bool to int as its incremented in PeerNetwork.cpp
* class to struct to match .cpp of UPnP in PeerNetwork.h
* Add missing return to string case in RLP.toBytesConstRef
Merge pull request #11 from SharpCoiner/patch-1

Update BUILDING.md
Merge pull request #12 from danielhams/master

Little fixes found using clang on OSX10.9:
Move towards more flexible cryptopp discovery.
#6 mavericks: expand [] operator due to clang bug on latest mavericks/xcode systems.
spaces to tabs
Merge pull request #14 from subtly/master

 Compiler/C++11 bug building on macos (Mavericks)
Merge branch 'master' of github.com:ethereum/cpp-ethereum
Make patch comply with coding standards.
Changed README.
Root bug fix.
Introduce a list of addresses to reject during interface endpoint discovery.
On MacOSX the loopback device is lo0, not lo, plus there are multicast bridges
which cause issues too.
Fixed locating cryptopp in system locations
Look at the contents of CMake variables
Old habits getting in the way. Formatting fixes.
Do not assume that the build dir is called cpp-ethereum-build.
Fixed typo.
Merge pull request #23 from SharpCoiner/buildpatch

Do not assume that the build dir is called cpp-ethereum-build.
Merge pull request #20 from danielhams/master

Reject local addresses during interface discovery