Comments, rearranging calls for readability

configure.ac

@@ -81,8 +81,8 @@ AC_F77_WRAPPERS         # Discover how to call F77 funcs from C, set F77_FUNC ma
 
 # Discover flags for Fortran preprocessing
 FC_temp="$F77"; FC="$F77"
-AC_FC_PP_SRCEXT([f])
-AC_FC_PP_DEFINE
+AC_FC_PP_SRCEXT([f])  # Discover what flags are needed to preprocess .f files
+AC_FC_PP_DEFINE       # Discover the flag (eg, -D, -Df) is used to define PP symbols
 FC="$FC_temp"
 
 ###############################################################################
@@ -94,6 +94,11 @@ if test "$ac_cv_sizeof_int_p" -eq 8; then
   AC_DEFINE([PTRSIZE8], 1, [If sizeof *int is 8])
 fi
 
+# See if 'underscore' is in mangling scheme.  
+if echo "foobar"| tr -d @<:@:blank:@:>@ | grep '\<underscore\>' > /dev/null ; then 
+  AC_DEFINE([UNDERSCORE], 1, [If Fortran name-mangling scheme adds an underscore])
+fi
+
 # See if MPI is enabled
 if test "$mpi" = "yes"; then
   AC_DEFINE([MPI], 1, [If MPI is enabled])
@@ -109,11 +114,6 @@ if test "$ac_cv_sizeof_long_int" -eq 8; then
   AC_DEFINE([LONGINT8], 1, [If sizeof long int is 8])
 fi
 
-# See if 'underscore' is in mangling scheme.  
-if echo "foobar"| tr -d @<:@:blank:@:>@ | grep '\<underscore\>' > /dev/null ; then 
-  AC_DEFINE([UNDERSCORE], 1, [If Fortran name-mangling scheme adds an underscore])
-fi
-
 # See if timer is enabled
 if test "$timer" = "no"; then
   AC_DEFINE([NOTIMER], 1, [If timer is disabled])