Bug 21000: Force case sensitivity on Getopt::Long

Bug 21000: Force case sensitivity on Getopt::Long

Before patch: -D and -d are mistaken for --debug

    $ sudo DEB_BUILD_OPTIONS=nocheck ./debian/build-git-snapshot -r ~/debian -v 19.06~git --autoversion -d -D="stretch"
    Option d does not take an argument
    git status --porcelain -unormal
    git rev-parse --short=8 HEAD
    dch --force-distribution -D "squeeze-dev" -v "19.06~git+20190627205913.466f99e4-1" "Building git snapshot."
    dch warning: Recognised distributions are:
    experimental, unstable, testing, stable, oldstable, oldoldstable,
    {bullseye,buster,stretch,jessie,wheezy}-proposed-updates,
    {testing,stable,oldstable,oldoldstable}-proposed-updates,
    {bullseye,buster,stretch,jessie,wheezy}-security,
    {testing,stable,oldstable,oldoldstable}}-security, jessie-backports, stretch-backports and UNRELEASED.
    Using your request anyway.

NOTE: squeeze-dev in the first dch line and warning about Option d.

Apply patch: -D and -d are differentiated correctly.
    $ sudo DEB_BUILD_OPTIONS=nocheck ./debian/build-git-snapshot -r ~/debian -v 19.06~git --autoversion -d -D="stretch"
    git status --porcelain -unormal
    git rev-parse --short=8 HEAD
    dch --force-distribution -D "stretch" -v "19.06~git+20190627210316.b3f919a7-1" "Building git snapshot."
    dch warning: Previous package version was Debian native whilst new version is not
    dch -r "Building git snapshot."

NOTE: No more 'Option d' error, and "stretch" in the first dch line.
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>