Payment Protocol: X509-validated payment requests

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.

share/qt/protobuf.pri

@@ -0,0 +1,35 @@
+# Based on: http://code.google.com/p/ostinato/source/browse/protobuf.pri
+#
+# Qt qmake integration with Google Protocol Buffers compiler protoc
+#
+# To compile protocol buffers with qt qmake, specify PROTOS variable and
+# include this file
+#
+# Example:
+# PROTOS = a.proto b.proto
+# include(protobuf.pri)
+#
+# Set PROTO_PATH if you need to set the protoc --proto_path search path
+# Set PROTOC to the path to the protoc compiler if it is not in your $PATH
+#
+
+isEmpty(PROTO_DIR):PROTO_DIR = .
+isEmpty(PROTOC):PROTOC = protoc
+
+PROTOPATHS =
+for(p, PROTO_PATH):PROTOPATHS += --proto_path=$${p}
+
+protobuf_decl.name  = protobuf header
+protobuf_decl.input = PROTOS
+protobuf_decl.output  = $${PROTO_DIR}/${QMAKE_FILE_BASE}.pb.h
+protobuf_decl.commands = $${PROTOC} --cpp_out="$${PROTO_DIR}" $${PROTOPATHS} --proto_path=${QMAKE_FILE_IN_PATH} ${QMAKE_FILE_NAME}
+protobuf_decl.variable_out = GENERATED_FILES
+QMAKE_EXTRA_COMPILERS += protobuf_decl
+
+protobuf_impl.name  = protobuf implementation
+protobuf_impl.input = PROTOS
+protobuf_impl.output  = $${PROTO_DIR}/${QMAKE_FILE_BASE}.pb.cc
+protobuf_impl.depends  = $${PROTO_DIR}/${QMAKE_FILE_BASE}.pb.h
+protobuf_impl.commands = $$escape_expand(\\n)
+protobuf_impl.variable_out = GENERATED_SOURCES
+QMAKE_EXTRA_COMPILERS += protobuf_impl