enable md5sum digest verification

all (well I just checked LOS, aoscp and aicp) ROM scripts use
"md5sum" as extension but TWRP checks only for the extension
"md5".
This change will also expects md5sum as the default digest extension
and only if not found falling back to md5.

Change-Id: Ia1dd072d77d53ed6c6ff13c6db730abdcdb56bb3
diff --git a/twinstall.cpp b/twinstall.cpp
index 7351e63..d63088c 100644
--- a/twinstall.cpp
+++ b/twinstall.cpp
@@ -327,7 +327,14 @@
 		string digest_str;
 		string Full_Filename = path;
 		string digest_file = path;
-		digest_file += ".md5";
+		string defmd5file = digest_file + ".md5sum";
+
+		if (TWFunc::Path_Exists(defmd5file)) {
+			digest_file += ".md5sum";
+		}
+		else {
+			digest_file += ".md5";
+		}
 
 		gui_msg("check_for_digest=Checking for Digest file...");
 		if (!TWFunc::Path_Exists(digest_file)) {