BUG #12858: Server crash on upgrade due to invalid timezoneset syntax

The following bug has been logged on the website:

Bug reference:      12858
Logged by:          Tyler Poland
Email address:      tpoland@engineyard.com
PostgreSQL version: 9.1.15
Operating system:   Gentoo Linux
Description:

Immediately after upgrading from 9.1.9 to 9.1.15 the server (still running
9.1.9) crashes with the error:

2015-03-12 18:39:55.585 UTC,,,13721,,5500d157.3599,9,,2015-03-11 23:35:51
UTC,,0,FATAL,22023,"invalid number for time zone offset in time zone file
""Default"", line 57",,,,,,,,,""

Reviewing the Default timezoneset file reveals that it has changed from:

````

### Before

ART    -10800    # Argentina Time
                 #     (America/Argentina/Buenos_Aires)
                 #     (America/Argentina/Cordoba)
                 #     (America/Argentina/Tucuman)
                 #     (America/Argentina/La_Rioja)
                 #     (America/Argentina/San_Juan)
                 #     (America/Argentina/Jujuy)
                 #     (America/Argentina/Catamarca)
                 #     (America/Argentina/Mendoza)
                 #     (America/Argentina/Rio_Gallegos)
                 #     (America/Argentina/Ushuaia)
ARST    -7200 D  # Argentina Summer Time
````

To
````
ART    America/Argentina/Buenos_Aires  # Argentina Time
                 #     (America/Argentina/Buenos_Aires)
                 #     (America/Argentina/Cordoba)
                 #     (America/Argentina/Tucuman)
                 #     (America/Argentina/La_Rioja)
                 #     (America/Argentina/San_Juan)
                 #     (America/Argentina/Jujuy)
                 #     (America/Argentina/Catamarca)
                 #     (America/Argentina/Mendoza)
                 #     (America/Argentina/Rio_Gallegos)
                 #     (America/Argentina/Ushuaia)
ARST    America/Argentina/Buenos_Aires  # Argentina Summer Time
````