[binutils-gdb] No longer handle negative 'step' in 'proceed'

[sergiodj+buildbot@redhat.com]

*** TEST RESULTS FOR COMMIT 3333f03ae1b02b321717b4bc4887201ed4fc6a26 ***

Author: Pedro Alves <palves@redhat.com>
Branch: master
Commit: 3333f03ae1b02b321717b4bc4887201ed4fc6a26

No longer handle negative 'step' in 'proceed'
Nothing ever passes a negative 'step' to proceed.
Gets rid of one of the few remaining stop_after_trap references.

gdb/ChangeLog
2015-03-24  Pedro Alves  <palves@redhat.com>

	* infrun.c (proceed): No longer handle negative step.