require automake >= 1.15

Fixes a potential "arg list too long" error at make time. See
https://lists.gnu.org/archive/html/bug-automake/2014-10/msg00009.html


for more info. Closes #2215
Signed-off-by: Wesley Bland <wbland@anl.gov>

autogen.sh

@@ -506,7 +506,7 @@ fi
 
 echo_n "Checking for automake version... "
 recreate_tmp
-ver=1.12.3
+ver=1.15
 cat > .tmp/configure.ac<<EOF
 AC_INIT(testver,1.0)
 AC_CONFIG_AUX_DIR([m4])