Expire header is hard-coded as 1997 in common_lib.inc

[imkalvin]

Description

We observe the jsonResult.php will always return a response header 'expires:
Sat, 26 Jul 1997 05:00:00 GMT'

With some study in code, we found it was caused by
98dfcc1

Steps to reproduce

Every single call to jsonResult will return with this header :)

Expected result

Should be sometime say 7 days from now ?

Actual result

hard-coded 'Sat, 26 Jul 1997 05:00:00 GMT'

[imkalvin]

#3149 was created which will return the expire header as 7 days later.