Fix behaviour of p7_trace_Compare on failed comparison

[althonos]

p7_trace_Compare is a comparison function and is reported to return eslOK on equality and eslFAIL otherwise, like other comparison functions (e.g. p7_hmm_Compare). This is also the intended behaviour according to the function documentation:

hmmer/src/p7_trace.c

Lines 788 to 793 in bb7c3e1

	/* Function: p7_trace_Compare()
	* Synopsis: Compare two traces for identity
	* Incept: SRE, Wed Aug 20 09:05:24 2008 [Janelia]
	*
	* Purpose: Compare two tracebacks; return <eslOK> if they
	* are identical, <eslFAIL> if not.

However, the current implementation instead calls esl_fatal on any failed equality test and exits the current process.

This is not really a problem anywhere given that AFAICT p7_trace_Compare is only used in unit tests (where the failed comparison would then trigger the same esl_fatal("FAIL") call anyway), but I noticed in PyHMMER after trying to use p7_trace_Compare to compare traces and seeing my test program forcefully exit.