Coding Challenge #2

The Task

Leading on from the first challenge.

Write some code to output all letters of the alphabet from a-z and back down to a in lowercase. Then b-z in uppercase back to a in uppercase too. The output should be:

If you want your solution benchmarked against others, please provide it in PHP (benchmarking PHP vs JS is too much hassle!)

abcdefghijklmnopqrstuvwxyzyxwvutsrqponmlkjihgfedcbaBCDEFGHIJKLMNOPQRSTUVWXYZYXWVUTSRQPONMLKJIHGFEDCBA

Post all solutions below, fastest and shortest solution wins.