Restores maintainer mode in the autotools (#200)

Maintainer mode should be enabled in development branches.

Also adds helpful commenting.

configure.ac

@@ -37,18 +37,46 @@ AC_CONFIG_MACRO_DIR([m4])
 AM_INIT_AUTOMAKE([foreign subdir-objects])
 m4_ifdef([AM_SILENT_RULES], [AM_SILENT_RULES([yes])]) # use silent rules where available - automake 1.11
 
-## AM_MAINTAINER_MODE turns off "rebuild rules" that contain dependencies
-## for Makefiles, configure, src/H5config.h, etc. If AM_MAINTAINER_MODE
-## is enabled, these files will be rebuilt if out of date. This is a
-## problem because if users try to build on a machine with
-## the wrong versions of autoconf and automake, these files will be
-## rebuilt with the wrong versions and bad things can happen.
-## Also, CVS doesn't preserve dependencies between timestamps, so
-## Makefiles will often think rebuilding needs to occur when it doesn't.
+## AM_MAINTAINER_MODE determines the behavior of "rebuild rules" that contain
+## dependencies for Makefile.in files, configure, src/H5config.h, etc. If
+## AM_MAINTAINER_MODE is enabled, these files will be rebuilt if out of date.
+## When disabled, the autotools build files can get out of sync and the build
+## system will not complain or try to regenerate downstream files.
 ##
-## By default, it is enabled. Users can configure with
-## --disable-maintainer-mode to prevent running the autotools.
-AM_MAINTAINER_MODE([disable])
+## The AM_MAINTAINER_MODE macro also determines whether the
+## --(enable|disable)-maintainer-mode configure option is available. When the
+## macro is present, with or without a parameter, the option will be added
+## to the generated configure script.
+##
+## In summary:
+##
+##  AM_MAINTAINER_MODE([enable])
+##      - Build dependencies ON by default
+##      - Configure option exists
+##
+##  AM_MAINTAINER_MODE([disable])
+##      - Build dependencies OFF by default
+##      - Configure option exists
+##
+##  AM_MAINTAINER_MODE
+##      - Build dependencies OFF by default
+##      - Configure option exists
+##
+##  No AM_MAINTAINER_MODE macro
+##      - Build dependencies ON by default
+##      - No configure option to control build dependencies
+##
+## The biggest concern for us is that version control systems like git
+## usually don't preserve dependencies between timestamps, so the build
+## system will often think that upstream build files like Makefile.am are
+## dirty and that rebuilding needs to occur when it doesn't. This is a problem
+## in release branches where we provide the autotools-generated files. Users
+## who don't have autoconf, automake, etc. will then have difficulty building
+## release branches checked out from git.
+##
+## By default, maintainer mode is enabled in development branches and disabled
+## in release branches.
+AM_MAINTAINER_MODE([enable])
 
 ## ----------------------------------------------------------------------
 ## Set prefix default (install directory) to a directory in the build area.