time: MeST is a time zone name

Not only ChST but also MeST (America/Metlakatla) is a zone
name containing a lower case letter.

LGTM=robert.hencke, r
R=golang-codereviews, robert.hencke, bradfitz, r
CC=golang-codereviews
https://golang.org/cl/99910043

src/pkg/time/format.go

@@ -1037,8 +1037,8 @@ func parseTimeZone(value string) (length int, ok bool) {
 	if len(value) < 3 {
 		return 0, false
 	}
-	// Special case 1: This is the only zone with a lower-case letter.
-	if len(value) >= 4 && value[:4] == "ChST" {
+	// Special case 1: ChST and MeST are the only zones with a lower-case letter.
+	if len(value) >= 4 && (value[:4] == "ChST" || value[:4] == "MeST") {
 		return 4, true
 	}
 	// Special case 2: GMT may have an hour offset; treat it specially.

src/pkg/time/format_test.go

@@ -331,6 +331,7 @@ var parseTimeZoneTests = []ParseTimeZoneTest{
 	{"GMT-5 hi there", 5, true},
 	{"GMT-51 hi there", 3, true},
 	{"ChST hi there", 4, true},
+	{"MeST hi there", 4, true},
 	{"MSDx", 3, true},
 	{"MSDY", 0, false}, // four letters must end in T.
 	{"ESAST hi", 5, true},