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/mk-errno-list	Tue Feb 16 17:57:07 2016 -0800
+++ b/libinterp/mk-errno-list	Tue Feb 16 18:36:00 2016 -0800
@@ -24,7 +24,7 @@
 fi
 
 if [ $1 = "--perl" ]; then
-  PERL="$2";
+  PERL="$2"
   $PERL -e 'foreach $key (keys(%!)) {
     $x .= "#if defined ($key)\n    { \"$key\", $key, },\n#endif\n";
   }
@@ -34,7 +34,7 @@
   }'
 
 elif [ $1 = "--python" ]; then
-  PYTHON="$2";
+  PYTHON="$2"
   $PYTHON -c '
 from errno import errorcode
 from sys import stdin