Use abstract_clock and improved tests, in ResourceManager

Conflicts:
	Builds/VisualStudio2012/RippleD.vcxproj.filters

src/ripple/resource/api/Types.h

@@ -26,9 +26,6 @@ namespace Resource {
 struct Key;
 struct Entry;
 
-/** Measures seconds from an unspecified fixed reference event in the past. */
-typedef int DiscreteTime;
-
 }
 }