doc: Simple grammar fix

[Elias Benali]

Shouldn't the correct usage be "the number and aggregate size of
diversions are limited" instead of "is limited" ?
If so a patch is included to fix it.
Regards.

--------

diff -r -u m4-1.4.13.orig/doc/m4.info-1 m4-1.4.13/doc/m4.info-1
--- m4-1.4.13.orig/doc/m4.info-1        2009-03-31 22:22:01.000000000 -0400
+++ m4-1.4.13/doc/m4.info-1     2009-06-24 22:07:45.152490773 -0400
@@ -4215,7 +4215,7 @@
 in memory, freeing this memory for other diversions.  When creating the
 temporary file, `m4' honors the value of the environment variable
 `TMPDIR', and falls back to `/tmp'.  So, it is theoretically possible
-that the number and aggregate size of diversions is limited only by
+that the number and aggregate size of diversions are limited only by
 available disk space.

    Diversions make it possible to generate output in a different order
diff -r -u m4-1.4.13.orig/doc/m4.texinfo m4-1.4.13/doc/m4.texinfo
--- m4-1.4.13.orig/doc/m4.texinfo       2009-03-05 07:46:01.000000000 -0500
+++ m4-1.4.13/doc/m4.texinfo    2009-06-24 22:07:07.066360269 -0400
@@ -5100,7 +5100,7 @@
 When creating the temporary file, @code{m4} honors the value of the
 environment variable @env{TMPDIR}, and falls back to @file{/tmp}.
 So, it is theoretically possible that the number and aggregate size of
-diversions is limited only by available disk space.
+diversions are limited only by available disk space.

 @ignore
 @comment We need to test spilled diversions, but don't need to expose