don't assume that rev is a SHA1 hash

This was a problem when writing a fetcher that uses e.g. sha256 hashes
for revisions. This doesn't actually do anything new, but allows for
creating such fetchers in the future (perhaps when support for Git's
SHA256 object format gains more popularity).

src/libutil/hash.cc

@@ -155,7 +155,7 @@ static std::pair<std::optional<HashType>, bool> getParsedTypeAndSRI(std::string_
 {
     bool isSRI = false;
 
-    // Parse the has type before the separater, if there was one.
+    // Parse the hash type before the separator, if there was one.
     std::optional<HashType> optParsedType;
     {
         auto hashRaw = splitPrefixTo(rest, ':');