options: tiny simplification in dealing with erroneous opts

options: tiny simplification in dealing with erroneous opts

* lib/Automake/Options.pm (_process_option_list): Here, when an
invalid option is detected, there's no need to call &error with
the "uniq_scope => US_GLOBAL" switch.  In fact, if the same
erroneous option is specified in AUTOMAKE_OPTIONS in both (say)
'Makefile.am' and 'sub/Makefile.am', we want each such erroneous
usage reported separately, rather than just the first time it is
encountered (as happens when "uniq_scope => US_GLOBAL" is used).

Signed-off-by: Stefano Lattarini <stefano.lattarini@gmail.com>