Renaming execution strategy classes.
Changing all variables called action and func to operation.
Improving the exception messages related to execution strategies.
Improving the XML documentation related to execution strategies.

Work item: 1273
Migrations: Fix for #1251 - CF Stored Proc :: Invalid migration created when mapping entity with inheritance

Problem: When performing sproc body SQL gen, we were incorrectly dealing with discriminators by lifting the corresponding DbConstant expressions into parameters. However, for sproc bodies the discriminator values need to remain inlined as they are never passed as parameters by the runtime - They are effectively hard-coded because of the one-sproc-per-entity-type rule.
Solution: For sprocs we don't actually need to do parameter lifting in SQL gen because we do the lifting earlier, as part of the dynamic-to-function command tree conversion process. I disabled the lifting on the insert gen code-path as that's the only one relevant for discriminators.

Work Item: 1251
Migrations: Fix for #1246 - EF Stored Procs :: mapping Many-Many relationship when one class is abstract throws

Problem: When faking association ends during modification command tree generation, we were incorrectly attempting to activate abstract end types.
Solution: When activating ends, if the target type is abstract, then activate the first non-abstract derived type instead.

Work Item: 1246
Issue 1204 - update EntityConnection to no longer throw an exception if
you attempt to reopen an already-open connection
Merge branch 'master' of https://git01.codeplex.com/entityframework