Add CST (China Standard Time) to our lists of timezone abbreviations.

For some reason this seems to have been missed when the lists in
src/timezone/tznames/ were first constructed.  We can't put it in Default
because of the conflict with US CST, but we should certainly list it among
the alternative entries in Asia.txt.  (I checked for other oversights, but
all the other abbreviations that are in current use according to the IANA
files seem to be accounted for.)  Noted while responding to bug #12326.

src/timezone/tznames/America.txt

@@ -137,11 +137,13 @@ COT    -18000    # Columbia Time (not in zic)
 # Other timezones:
 #  - CST: Central Standard Time (Australia)
 #  - CST: Central Standard Time (America)
+#  - CST: China Standard Time (Asia)
 CST    -18000    # Cuba Central Standard Time (America)
                  #     (America/Havana)
 # CONFLICT! CST is not unique
 # Other timezones:
 #  - CST: Central Standard Time (Australia)
+#  - CST: China Standard Time (Asia)
 #  - CST: Cuba Central Standard Time (America)
 CST    -21600    # Central Standard Time (America)
                  #     (America/Cancun)

src/timezone/tznames/Asia.txt

@@ -59,6 +59,15 @@ CHOST   36000 D  # Choibalsan Summer Time (obsolete)
 CHOT    Asia/Choibalsan  # Choibalsan Time
                  #     (Asia/Choibalsan)
 CIT     28800    # Central Indonesia Time (obsolete, WITA is now preferred)
+# CONFLICT! CST is not unique
+# Other timezones:
+#  - CST: Central Standard Time (Australia)
+#  - CST: Central Standard Time (America)
+#  - CST: Cuba Central Standard Time (America)
+CST     28800    # China Standard Time
+                 #     (Asia/Macau)
+                 #     (Asia/Shanghai)
+                 #     (Asia/Taipei)
 EEST    10800 D  # East-Egypt Summer Time
                  # Eastern Europe Summer Time
                  #     (Africa/Cairo)

src/timezone/tznames/Australia.txt

@@ -41,6 +41,7 @@ CAST    34200    # Central Australia Standard Time (not in zic)
 # CONFLICT! CST is not unique
 # Other timezones:
 #  - CST: Central Standard Time (America)
+#  - CST: China Standard Time (Asia)
 #  - CST: Cuba Central Standard Time (America)
 CST     34200    # Central Standard Time (not in zic)
 CWST    31500    # Central Western Standard Time (not in zic)

src/timezone/tznames/Default

@@ -105,6 +105,7 @@ CLT    -14400    # Chile Time
 # CONFLICT! CST is not unique
 # Other timezones:
 #  - CST: Central Standard Time (Australia)
+#  - CST: China Standard Time (Asia)
 #  - CST: Cuba Central Standard Time (America)
 CST    -21600    # Central Standard Time (America)
                  #     (America/Cancun)