Fix 32 - add general check for escaping typars to check phase

This (partly) addresses the class of conditions like dotnet/fsharp#32
which give "undefined type variable" internal errors by adding
an earlier check to check.fs which gives a user-visible error in
this case.

These conditions can in some cases indicate problems with type
inference, though in the case of dotnet/fsharp#32 the check is actually the
best way to detect the escape condition.

fixes dotnet/fsharp#32
closes dotnet/fsharp#442

commit 5d4d818af94242b8f0594450721378762e6fe876
Merge: 3c3708f 0b88185
Author: Don Syme <donsyme@fastmail.fm>
Date:   Tue May 19 14:33:37 2015 +0100

    merge fsharp4

commit 3c3708fda6d0c16c45f68caed09a05a38c41f746
Author: Don Syme <donsyme@fastmail.fm>
Date:   Tue May 19 14:31:06 2015 +0100

    normalzie equi-recursive

commit 220131b3c88e149f3e6890da46de31d748233b54
Author: Don Syme <donsyme@fastmail.fm>
Date:   Tue May 12 15:32:07 2015 +0100

    update tests, change warning to error

commit 53153b8b1d60a50eb91f43b1f78bfda99d3a4a87
Author: Don Syme <donsyme@fastmail.fm>
Date:   Tue May 12 15:01:44 2015 +0100

    add general check for escaping typars to check phase

Author: dsyme

src/fsharp/FSComp.txt

@@ -1342,3 +1342,5 @@ estApplyStaticArgumentsForMethodNotImplemented,"A type provider implemented GetS
 3184,ppparsIncompleteExpression,"Incomplete preprocessor expression"
 3185,ppparsMissingToken,"Missing token '%s' in preprocessor expression"
 3186,pickleMissingDefinition,"An error occurred while reading the F# metadata node at position %d in table '%s' of assembly '%s'. The node had no matching declaration. Please report this warning. You may need to recompile the F# assembly you are using."
+3187,checkNotSufficientlyGenericBecauseOfScope,"Type inference caused the type variable %s to escape its scope. Consider adding an explicit type parameter declaration or adjusting your code to be less generic."
+3188,checkNotSufficientlyGenericBecauseOfScopeAnon,"Type inference caused an inference type variable to escape its scope. Consider adding type annotations to make your code less generic."