Allow PathInput to take an optional frequency parameter.

The previous version hard-coded the cache check frequency to 30
seconds.  This meant that the path was checked very frequently (max of
30 seconds and the evaluation period of the job), which could be
problematic for URL PathInput specifications, and especially ones that
are automatically updated frequently without *each* update necessarily
being interesting (an example: the haskell hackage index file.)

src/lib/Hydra/Plugin/PathInput.pm

@@ -11,12 +11,22 @@ sub supportedInputTypes {
     $inputTypes->{'path'} = 'Local path';
 }
 
+sub _parseValue {
+    my ($value) = @_;
+    my @parts = split ' ', $value;
+    (my $uri, my $freq) = @parts;
+    # by default don't check a path more often than every 30 seconds,
+    # but the second path argument can change that value.
+    $freq = defined $freq ? $freq : 30;
+    return ($uri, $freq);
+}
+
 sub fetchInput {
     my ($self, $type, $name, $value) = @_;
 
     return undef if $type ne "path";
 
-    my $uri = $value;
+    my ($uri, $timeout) = _parseValue($value);
 
     my $timestamp = time;
     my $sha256;