Improve .render performance

[cagmz]

I used ruby-prof to analyze the time spent in methods and memoized the most expensive ones. There is a space tradeoff but it may be worth the time gains.

Benchmarking script

Full output from script

Master Prepared Object Ruby prof call tree Fork Prepared Object Ruby prof call tree

Master ActiveRecord Ruby prof call tree Fork ActiveRecord Ruby prof call tree

IPS

	IPS (object)	IPS (ActiveRecord)
master	11776.2	10003.1
fork	12880.6	10821.8
diff	+ 9.378%	+ 8.184%

Memory

	Memory allocated (object)	Memory allocated (ActiveRecord)
master	53278996 bytes (712340 objects)	44599596 bytes (594605 objects)
fork	51929108 bytes (694292 objects)	48724236 bytes (649595 objects)
diff	- 2.534%	+ 9.248 %