Add support for .include directive in config files

Either files or directories of *.cnf or *.conf files
can be included.
Recursive inclusion of directories is not supported.

Reviewed-by: Andy Polyakov <appro@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/5351)

apps/openssl-vms.cnf

diff --git a/apps/openssl-vms.cnf b/apps/openssl-vms.cnf
index a3ca393..f4a2511 100644
--- a/apps/openssl-vms.cnf
+++ b/apps/openssl-vms.cnf
@@ -3,6 +3,10 @@
 # This is mostly being used for generation of certificate requests.
 #
 
+# Note that you can include other files from the main configuration
+# file using the .include directive.
+#.include filename
+
 # This definition stops the following lines choking if HOME isn't
 # defined.
 HOME			= .

apps/openssl.cnf

diff --git a/apps/openssl.cnf b/apps/openssl.cnf
index 32ee9e9..7d1a8bb 100644
--- a/apps/openssl.cnf
+++ b/apps/openssl.cnf
@@ -3,6 +3,10 @@
 # This is mostly being used for generation of certificate requests.
 #
 
+# Note that you can include other files from the main configuration
+# file using the .include directive.
+#.include filename
+
 # This definition stops the following lines choking if HOME isn't
 # defined.
 HOME			= .