Use --short form of git hash.  Use output from "git describe" for tag.

Expected outputs:
1. previous hg
2. previous git
3. updated git

Release (tagged) build:
1. Python 3.7.0a0 (v3.7.0a0:4def2a2901a5, ...
2. Python 3.7.0a0 (v3.7.0a0^0:05f53735c8912f8df1077e897f052571e13c3496, ...
3. Python 3.7.0a0 (v3.7.0a0:05f53735c8, ...

Development build:
1. Python 3.7.0a0 (default:41df79263a11, ...
2. Python 3.7.0a0 (master:05f53735c8912f8df1077e897f052571e13c3496, ...
3. Python 3.7.0a0 (heads/master-dirty:05f53735c8, ...

"dirty" means the working tree has uncommitted changes.
See "git help describe" for more info.
(cherry picked from commit 554626ada769abf82a5dabe6966afa4265acb6a6)
(cherry picked from commit e9213d929d7b0075539e87416f6a6fb86c27454b)

(cherry picked from commit 9cd5e87bac51d7b901e3c36bf22728bb1693da59)

Directory and zipfile execution previously added
the parent directory of the directory or zipfile
as sys.path[0] and then subsequently overwrote
it with the directory or zipfile itself.

This caused problems in isolated mode, as it
overwrote the "stdlib as a zip archive" entry
in sys.path, as the parent directory was
never added.

The attempted fix to that issue in bpo-29319
created the opposite problem in *non*-isolated
mode, by potentially leaving the parent
directory on sys.path instead of overwriting it.

This change fixes the root cause of the problem
by removing the whole "add-and-overwrite" dance
for sys.path[0], and instead simply never adds
the parent directory to sys.path in the first
place.
(cherry picked from commit d2977a3ae2cc6802921b1e3b6e9d13fcfbda872d)

(cherry picked from commit c60948464fb0ec116ea227f6bce8a4bb8fb75257)

(cherry picked from commit 51b646a55a4a1c4d0df764c4404a062fbcc6b356)

(cherry picked from commit 2225ddaa9e64c086b2b6997b0c9ac50921f7aa85)
(cherry picked from commit 4e1a065c20856a00d0fe88ce022b249170608058)

(cherry picked from commit e544b40faa5ab61b6aba691577d90b2b641f664d)