Fix a bug where a check was omitted
Add a function to find identifier at position

Where position is given as an int*int rather than a pos
Test and code for scoping rules of nested modules

The declarations contained in the modules should be nested.
Remove range from FindIdentiferFromTuple

It only returns the name, but no longer needs the caller to reference
FSharp.Compiler.Editor
Fix an off-by-one error in column number
IsValid should return true if identifier unchanged
Don't reject pointless renames