Entry_#copy_metadata has a nasty bug that makes copying symlinks
across filesystems fail. This lasted all the way through 1.9.3p194
before *finally* being fixed. This backports the official fix.
FixesHomebrew/homebrew#14710.
All logs are now stored from each command executed in Formula.install.
Error output is truncated to five lines in an attempt to not overwhelm the user and to encourage users to read the error output and report the bug properly. Maybe we can get that figure up from 70% to 90%.