setup-msysgit: Also set https_proxy

The URLs for the cloned repositories are now HTTPS URLs, therefore we
need to use the proxy also for such URLs if a proxy is required for
cloning to work.
setup-msysgit: avoid using the dashed form

It has been deprecated for quite a while now...

Besides, it does not seem to work here:
ln: accessing `//installer-tmp/bin/git.exe': No such host or network path
ln: accessing `//installer-tmp/bin/git.exe': No such host or network path
...
Merge pull request #197 from nilleb/patch-1

Issue 196, work in progress
--force: Propagate to shears.sh

After an annoying mistake and subsequent abort during a merging-rebase, I used the --force only to be stopped by a message from shears.sh telling me to use --force.

(As a side note, this commit could only have been made more amusing by submitting it yesterday...)
Merge pull request #199 from stuyvenberg/patch-1

--force: Propagate to shears.sh