Compile fix: forgotten parentheses around value
rename configure.in to configure.ac

It seems autoheader version 2.69 does not work with configure.in file,
and AM_CONFIG_HEADER macro.

aclocal: warning: autoconf input should be named 'configure.ac', not 'configure.in'
configure.in:585: warning: macro 'AM_CONFIG_HEADER' not found in library
Executing:  autoheader

autoheader: error: AC_CONFIG_HEADERS not found in configure.in
fix 'make distcheck' which had out-of-tree build issue
utils: remove bashisms

fbsetbg: The random number generation used 'time' shell internal, which
does not exist in all shells.  Allowing 'ps' output to be part of cksum
input will increase entropy and enhance quality of the randomness.

fbsetbg: The second fix is more important.  In posix shell there is no
'==' comparision operator.

fluxbox-generate_menu: There are no quarantees about echo accepting
options, so use 'printf' for more advanced outputing.
util/fluxbox-generate_menu: default browswer variable can be empty

Noticed when debugging in mac.
do not try to reach $(top_srcdir)/.git directory contents when building a release tar ball