Minor optimization in time caching code.

Reduced the size of the cached string buffer from 128 to 32, which is
still larger than the largest possible time string, which is 26
characters.

Added a check for the user passing in an output buffer that is smaller
than the cached string. Previously, the code would have copied past
the end of the users buffer.
Bug #948: detect thread local storage support
Use wget or curl to download ruleset.