[git] Update aliases

“cm” for “commit -m”, “d” replaces ”df”, “st” removed since it
duplicates “s”, and finally adjust the format of “l”.
[git] Remove unused setting

“shallow” is the default for threading in git-format-patch.
[shell] Update git prompt
[shell] Update cd to support passing a file name

If file name is passed instead of a directory name, the cd function
will go to the directory that contains that file (i.e. it's basename).
This is particularly useful with history substitution.
[shell] Add “@” alias for “for i in”

This may look a bit weird, but it saves some typing.
[git] Set up git-credential-netrc helper
[emacs] Fix corp laptop checking code
[emacs] Tiny setting refactoring
[email] Update signing set-up

pgg and pgg-gpg packages are not deprecated.