Make sure redirected stdout and stderr share the same offset

This fixes broken output like this:

  Error: No such file or directory - non_existent_file
  ee/src/tree-1.7.0.tgz
  Already downloaded: /Library/Caches/Homebrew/tree-1.7.0.tgz
  ==> Verifying tree-1.7.0.tgz checksum
  tar xf /Library/Caches/Homebrew/tree-1.7.0.tgz
Fix file descriptor leak in Formula#system
jpeg-turbo: adds mirror

In light of Sourceforge’s recent dip towards unreliability, this shoves
the official url onto a mirror and uses the Debian download link as the
primary driver. No other changes.
Jpeg-turbo: Added Mirror.

Adds a mirror to the jpeg-turbo formula.
jpeg-turbo: add 1.3.1 bottle.