Initial sort should be density based

Summary: The initial order of functions influences the final
clustering - so we should use samples/byte, not samples to
sort them.

Reviewed By: @ottoni

Differential Revision: D1657737

Signature: t1:1657737:1415119241:e145694681f86a14ae63a23f73a2011e1dfd6347
Add HH\int/float/bool typehints to PHP

Summary: - Support HH\(string|int|float|bool) in PHP without hhvm.force_hh
- (string|int|float|bool) in PHP without in hhvm.force_hh still refer to classes

These are not intended for direct usage by developers.

Mocking frameworks find the parameter typehints using reflection, then generate
mocks in PHP using the same typehint. 3 ways to fix this came to mind:

 - Always support HH\foo scalar typehints
 - Modify Reflection to not return these
 - Modify these mocking frameworks to filter out scalar typehints

This diff takes the first option.

fixes facebook/hhvm#4021

Reviewed By: @paroski

Differential Revision: D1642075

Signature: t1:1642075:1414634502:1901bd88b334adfa9b0b39925d706675892f6411