Switch the SplitKeyVal function to accept escapes

This tiny patch switches the SplitKeyVal function (and thus the command
line options like -H, -B, etc.) to UnescapeAndSplit, thus allowing one
to use escaped commas in the values of parameters.

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Guido Trotter <ultrotter@google.com>