parser: fix invalid segment override on EQU FAR pointers

[alexvoste]

The parser incorrectly treated colons as memory segment overrides inside EQU directives because of an inverted far_jmp_ok check. This regression was introduced in commit 8981724. Removing the incorrect negation restores proper parsing of FAR pointer constants.

Fixes #242

[hpax]

Rebased and committed.

[hpax]

This patch caused multiple tests to fail, because a segment override prefix was being dropped. Please make sure "make travis" patches before submitting a pull request.

I have reverted this patch, pending a proper fix.

[alexvoste]

@hpax I've addressed the segment override regression by refining the parser condition and ensured all local tests (including the failing obj and riprel tests) pass.

The CI checks are green. Please take another look.

[hpax]

Could you please add a proper commit message and Signed-off-by: line to your commit (see the SubmittingPatches file)?

I'm a bit confused about the asm/labels.c change; that looks like a separate memory leak fix? That is of course entirely legitimate (and appreciated), but it should be a separate patch with a separate patch description.

I really do appreciate your effort on this.

[hpax]

The SoB line is great, but a commit description is really valuable when trying to figure out 20 years from now what is broken when something needed to change.

A description of the problem and why the fix is the correct one would be really appreciated.