Two small fixes

[Vogtinator]

Do not overwrite manually specified release with autoprobe:

> txt2man -p tmp
.\" Text automatically generated by txt2man
.TH test 1 "16 Juni 2016" "txt2man" "Linux Reference Manual"

# Old behaviour
> txt2man -r "release" -p tmp
.\" Text automatically generated by txt2man
.TH test 1 "16 Juni 2016" "txt2man" "Linux Reference Manual"

# New behaviour
> ./txt2man -r "release" -p tmp
.\" Text automatically generated by txt2man
.TH test 1 "16 Juni 2016" "release" "Linux Reference Manual"

and also format the date in a locale-independant way, like with a manually specified one.

[mvertes]

Thanks for your contribution!