Makefile.local: Automatically use makefile mode

We add a magic line to the beginning of each Makefile.local file to
help the editor know that it should use makefile mode for editing the
file, (even though the filename isn't exactly "Makefile").

Edited-by: Carl Worth <cworth@cworth.org>: Expand treatment from
emacs/Makefile.local to each instance of Makefile.local.

Makefile.local

@@ -1,3 +1,5 @@
+# -*- makefile -*-
+
 # Here's the (hopefully simple) versioning scheme.
 #
 # Releases of notmuch have a two-digit version (0.1, 0.2, etc.). We

compat/Makefile.local

@@ -1,3 +1,5 @@
+# -*- makefile -*-
+
 dir := compat
 extra_cflags += -I$(dir)
 

emacs/Makefile.local

@@ -1,3 +1,5 @@
+# -*- makefile -*-
+
 dir := emacs
 emacs_sources := $(dir)/notmuch.el
 

lib/Makefile.local

@@ -1,3 +1,5 @@
+# -*- makefile -*-
+
 # The major version of the library interface. This will control the soname.
 # As such, this number must be incremented for any incompatible change to
 # the library interface, (such as the deletion of an API or a major