If exception has no message raise again

Shows full backtrace, which is useful. Now blank "raise" statements are the equivalent of admitting programmer error. The backtrace will be useful.

1 files changed, 1 insertions, 0 deletions

diff --git a/bin/brew b/bin/brew
index 27596b22e..efed2c8a5 100755
--- a/bin/brew
+++ b/bin/brew
@@ -109,6 +109,7 @@ rescue BuildError => e
   e.dump
   exit 1
 rescue RuntimeError, SystemCallError => e
+  raise if e.message.empty?
   onoe e
   puts e.backtrace if ARGV.debug?
   exit 1