--localtime: Use local time instead of UTC (include timezone abbrevation in the name)

[polletfa]

Yet another proposed solution for the date problem (#74), which also address the possible name collision because of DST.

The default behaviour is unchanged but a new option is added: -L or --localtime.
Ẃith this option, the local time is used and the timezone abbreviation is added to the name.
This avoid problems with DST and also avoid confusion when switching from UTC to local time.
The matching mechanism in do_snapshot to identify older snapshots was modified so as to match both formats (UTC without timezone indication and localtime with timezone) and also accept variable-length strings since the timezone abbreviation has variable length.

[hbh7]

Something of note is that if your default /bin/sh is dash (common on Debian, Ubuntu based systems, possibly others), then your line 211: if [ "${jj:0:${#trunc}}" = "$trunc" ] will fail and throw a Bad substitution error. Changing the shebang to /bin/bash solved this for me, although I think a more general solution would be something else.

Credit: https://stackoverflow.com/questions/20615217/bash-bad-substitution

[polletfa]

Thanks for the advice. I’ll see how I can rewrite it without bashism.