Timezone tests fail on Windows

[osteele]

See https://ci.appveyor.com/project/osteele/tuesday:

go test ./...
--- FAIL: TestStrftime (0.05s)
	Error Trace:	strftime_test.go:134
	Error:      	Not equal: 
	            	expected: "Mon Jan  2 15:04:05 EST 2006"
	            	actual: "Mon Jan  2 15:04:05  2006"
	Messages:   	Strftime "%+"
--- FAIL: TestStrftime_zones (0.00s)
	Error Trace:	strftime_test.go:207
	Error:      	Not equal: 
	            	expected: "%z=-0500 %Z=EST"
	            	actual: "%z=+0000 %Z=EST"
	Messages:   	02 Jan 06 15:04 EST
--- FAIL: ExampleStrftime_timezone (0.00s)
got:
EDT +0000 +00:00 +00:00:00

[osteele]

The issue was that setting the TZ environment variable has no effect on Windows.

The tests now pass if you set the timezone before running the tests, e.g. tzutil /s "Eastern Standard Time".

This fixes the appveyor, but is a gotcha for Windows development.

A fix is to remove the reliance on system timezone entirely, and update the tests to parse time strings in EST instead of local.