Uninitialized local variable

implicit_return_defaults is not properly initialized. I am implementing a MERGE statement (inherits from Executable and ClauseElement) that is neither INSERT nor UPDATE. This causes access to the uninitialized variable in line 1979.
Update compiler.py

Moved initialization into else block
Merge branch 'rel_0_9' of https://github.com/BY-jk/sqlalchemy into rel_0_9