Add new timezone abbrevation "FET".

This seems to have been invented in 2011 to represent GMT+3, non daylight
savings rules, as now used in Europe/Kaliningrad and Europe/Minsk.
There are no conflicts so might as well add it to the Default list.
Per bug #7804 from Ruslan Izmaylov.

src/timezone/tznames/Default

@@ -615,6 +615,9 @@ EETDST  10800 D  # East-Egypt Summertime
                  #     (Europe/Uzhgorod)
                  #     (Europe/Vilnius)
                  #     (Europe/Zaporozhye)
+FET     10800    # Further-eastern European Time
+                 #     (Europe/Kaliningrad)
+                 #     (Europe/Minsk)
 MEST     7200 D  # Middle Europe Summer Time (not in zic)
 MET      3600    # Middle Europe Time (not in zic)
 METDST   7200 D  # Middle Europe Summer Time (not in zic)

src/timezone/tznames/Europe.txt

@@ -154,6 +154,9 @@ EETDST  10800 D  # East-Egypt Summertime
                  #     (Europe/Uzhgorod)
                  #     (Europe/Vilnius)
                  #     (Europe/Zaporozhye)
+FET     10800    # Further-eastern European Time
+                 #     (Europe/Kaliningrad)
+                 #     (Europe/Minsk)
 GMT         0    # Greenwich Mean Time
                  #     (Africa/Abidjan)
                  #     (Africa/Bamako)