Bugzilla Bug 168253

There are two lines in the rpm2targz script which cause errors on g/fbsd due to
their incompatibility with fbsd's sh:

1] line 26 -> [ "$TMPDIR" == "" ] && TMPDIR=/tmp

   The correct expression, compatibile with the sh syntax, is with only one 
   equal sign, so:
   [ "$TMPDIR" = "" ] && TMPDIR=/tmp

2] line 91 -> if echo ${PAYLOADHEAD} | grep -e $'^\037\213' > /dev/null ; then

   This line fails due to the fact that the $'' construct is unsupported, as
   noted by exg, and therefore grep interprets \037 and \213 as backward
   expressions, instead of the considering the respective non-printable
   characters (which are the magic bytes of the gzip format).
   A possibile solution could be to filter PAYLOADHEAD trough `od -c` and then
   simply: grep -e '037.213'

However as Flameeyes noted, the most simple (yet effective) solution is to use
bash instead of sh to parse the script.

Reproducible: Always

Steps to Reproduce:

I have committed the fix; as with the new baselayout we might have more people
having /bin/sh not linked to bash, I've followed exg's suggestion and used od
-c.