maint: Use consistent coding style for build helper shell scripts * mk-octave-config-h.sh: Keep if-then on a single line. * move-if-change: Insert a space in interpreter directive for consistency. * build-env-features.sh, config-images.sh, config-module.sh, config-ops.sh, find-defun-files.sh, find-files-with-tests.sh, mk-errno-list, libinterp/mk-pkg-add, scripts/mk-pkg-add, mkbuiltins, mkdefs, mkdocs, mkf77def.in, mkops: Initialize environment variable defaults consistently. Use shift only when the argument list is not empty. Remove unnecessary quotes and semicolons on variable assignments. Insert/remove blank lines for consistency.

--- a/libinterp/mkdefs	Tue Feb 16 17:57:07 2016 -0800
+++ b/libinterp/mkdefs	Tue Feb 16 18:36:00 2016 -0800
@@ -18,7 +18,7 @@
 # along with Octave; see the file COPYING.  If not, see
 # <http://www.gnu.org/licenses/>.
 
-SED=${SED:-'sed'}
+SED=${SED:-sed}
 
 if [ $# -ne 2 ]; then
   echo "usage: mkdefs srcdir file < preprocessed-file-contents" 1>&2
@@ -26,7 +26,7 @@
 fi
 
 srcdir="$1"
-file="$2";
+file="$2"
 
 echo "// DO NOT EDIT!  Generated automatically by mkdefs."
 case "$file" in