RT2626: Change default_bits from 1K to 2K

This is a more comprehensive fix.  It changes all
keygen apps to use 2K keys. It also changes the
default to use SHA256 not SHA1.  This is from
Kurt's upstream Debian changes.

Reviewed-by: Rich Salz <rsalz@openssl.org>
Reviewed-by: Kurt Roeckx <kurt@openssl.org>
diff --git a/apps/gendh.c b/apps/gendh.c
index 4ec776b..8df8c62 100644
--- a/apps/gendh.c
+++ b/apps/gendh.c
@@ -78,7 +78,7 @@
 #include <openssl/x509.h>
 #include <openssl/pem.h>
 
-#define DEFBITS	512
+#define DEFBITS	2048
 #undef PROG
 #define PROG gendh_main