Configurable history size in master (#2606)

* split journaldb commit into two functions: journal_under and mark_canonical

* use new commit mechanism in client

* Configurable history size in master

* Reduce DB history

* Configurable history size

* Set min history size

* Test

* Fixed a test and reduced the limit

ethcore/src/block.rs

@@ -404,6 +404,10 @@ impl<'x> OpenBlock<'x> {
 			uncle_bytes: uncle_bytes,
 		}
 	}
+
+	#[cfg(test)]
+	/// Return mutable block reference. To be used in tests only.
+	pub fn block_mut (&mut self) -> &mut ExecutedBlock { &mut self.block }
 }
 
 impl<'x> IsBlock for OpenBlock<'x> {