Added ability for importing/exporting compressed/uncompressed wifs.  secret_to_wif is compressed by default.

Needs testing.
Bugfix: secret_to_wif now works correctly for compressed keys.
Bugfix: wif_to_secret now works correctly for compressed keys.
If a program imports a wif using this method then it should check the compressed flag itself and call elliptic_curve_key::set_secret with compressed flag set to false if compression is not used.
Added is_wif_compressed, checks the length of the wif and for the 0x01 compressed flag.
Does no other validity checks.
Fix examples/determ.cpp compile break and examples/makefile missing library.
Set the eckey to uncompressed when testing against the deterministic wallet.
port over mnemonic stuff from libbitcoin.
add mnemonic.hpp to wallet.hpp includes
Merge branch 'master' of git://github.com/evoskuil/libwallet into evoskuil-master

Conflicts:
	examples/determ.cpp