Description of problem:
xterm configure script fails in rawhide with an odd error:
line 5780: bad substitution: no closing `}' in ${icondir:-'\$(exec_prefix)/share/pixmaps'}

It seems that when bash is started as /bin/sh, the following expression doesn't work:

$ echo "${a:-'a/b'}"
sh: bad substitution: no closing `}' in ${a:-'a/b'}

Interesting is that removing the slash or the quotes or the double quotes from the expression makes it work.

Version-Release number of selected component (if applicable):
bash-4.2.0-0.1.rc2.fc15.x86_64

How reproducible:
Always

Steps to Reproduce:
1. echo "${a:-'a/b'}"

Actual results:
sh: bad substitution: no closing `}' in ${a:-'a/b'}

Expected results:
a/b