bug#39591: grep v3.4 after-context

[Adams, John]

Recent greps do not behave as documented with respect to after-context.  In the 
past I've been accustomed to -AX meaning print X lines of after context.  That 
is not how gnu grep is working now, but it is how it is documented.  In fact 
-AX, which I tested with a v3.4 that I build on Ubuntu 18, will print X+1 lines 
of after-context.  If you want 1, you must say -A0.