Add changes required by Nimble lock file support (#12104)

Implemented support for Nimble local cache with package directories with
a checksum of the package at the end of their names. Now the compiler
supports package paths in the form:

 * /path_to_nimble_cache_dir/pkgs/package_name-1.2.3-
FEBADEAEA2345E777F0F6F8433F7F0A52EDD5D1B

 * /path_to_nimble_cache_dir/pkgs/package_name-#head-
042D4BE2B90ED0672E717D71850ABDB0A2D19CD2

 * /path_to_nimble_cache_dir/pkgs/package_name-#branch-name-
DBC1F902CB79946E990E38AF51F0BAD36ACFABD9

Related to nim-lang/nimble#127

compiler/modulepaths.nim

@@ -21,7 +21,7 @@ when false:
     for k, p in os.walkDir(dir, relative=true):
       if k == pcDir and p.len > pkg.len+1 and
           p[pkg.len] == '-' and p.startsWith(pkg):
-        let (_, a) = getPathVersion(p)
+        let (_, a, _) = getPathVersionChecksum(p)
         if bestv.len == 0 or bestv < a:
           bestv = a
           best = dir / p