swiften: fix build

It was failing with:

  LINK Documentation/SwiftenDevelopersGuide/Examples/EchoBot/EchoBot0x
/nix/store/mgdjnsrkqgmxqjaqaxgqyqm7fwyi96fk-binutils-2.31.1/bin/ld: cannot find -lssl
/nix/store/mgdjnsrkqgmxqjaqaxgqyqm7fwyi96fk-binutils-2.31.1/bin/ld: cannot find -lcrypto
collect2: error: ld returned 1 exit status

pkgs/development/libraries/swiften/default.nix

@@ -12,6 +12,8 @@ stdenv.mkDerivation rec {
     sha256 = "0w0aiszjd58ynxpacwcgf052zpmbpcym4dhci64vbfgch6wryz0w";
   };
 
+  patches = [ ./scons.patch ];
+
   sconsFlags = [
     "openssl=${openssl.dev}"
     "boost_includedir=${boost.dev}/include"
@@ -23,12 +25,13 @@ stdenv.mkDerivation rec {
     installFlags+=" SWIFT_INSTALLDIR=$out"
   '';
 
+  enableParallelBuilding = true;
+
   meta = with stdenv.lib; {
     description = "An XMPP library for C++, used by the Swift client";
     homepage    = http://swift.im/swiften.html;
     license     = licenses.gpl2Plus;
     platforms   = platforms.linux;
     maintainers = [ maintainers.twey ];
-    broken = true; # TODO: Build is failing!
   };
 }

pkgs/development/libraries/swiften/scons.patch

@@ -0,0 +1,9 @@
+--- a/BuildTools/SCons/SConscript.boot
++++ b/BuildTools/SCons/SConscript.boot
+@@ -129,5 +129 @@ vars.Add(PathVariable("sparkle_public_dsa_key", "Optional path to a public DSA k
+-env_ENV = {
+-    'PATH' : os.environ['PATH'],
+-    'LD_LIBRARY_PATH' : os.environ.get("LD_LIBRARY_PATH", ""),
+-    'TERM' : os.environ.get("TERM", ""),
+-}
++env_ENV = os.environ