Fortran: Support fixed format source code

[stevewpalmer]

At the moment the Fortran lexical analyser does not support fixed format source where whitespace are insignificant. Although this is very rarely used and only has value when compiling ancient Fortran source code, it may be worth looking to see if we can implement a quick fix for completeness.

In particular, the following are all variables although they start with keywords:

DO 3 =   53.
CALL FL =62.
TYPE I = 63.
GO TO 1 = 4 3.

This causes the ValidateFixedFormat2 unit test to fail, along with several FCVS21 tests (which are presently disabled in the make run for this reason).