[xmlsec] xmlsec test harness

[Aleksey Sanin]

Hi, Tej!

Thanks for the patch! I have applied and checked it in with
minor modification: I don't think that it's a good idea to have
two copies of tests/test*.sh scripts. Instead I've added one more
command line option (key format: "der" or "pem")  to these
scripts and made "der" default in the Makefiles (i.e. removing
all "check-*-std" targets from Makefile). And one can still run
tests using pem files from a command line if needed.

Aleksey