tests should be able to use GNU grep

[rmottola]

if gnu grep is installed as ggrep, like we can use gmake, gtar...

otherwise e.g. on solaris we have infinite failures during test runs:

Usage: grep -hblcnsviw pattern file . . .
grep: illegal option -- a
Usage: grep -hblcnsviw pattern file . . .
grep: illegal option -- a
Usage: grep -hblcnsviw pattern file . . .
.....