+JH/14 Bug 2933: Fix regex substring match variables for null matches. Since 4.96
+ a capture group which obtained no text (eg. "(abc)*" matching zero
+ occurrences) could cause a segfault if the corresponding $<n> was
+ expanded.
+
+JH/15 Fix argument parsing for ${run } expansion. Previously, when an argument
+ included a close-brace character (eg. it itself used an expansion) an
+ error occurred.
+