hgk: fix tag list parser (issue4101)

As tags may have embedded spaces, and "hg tags" command doesn't escape them,
the output of the command doesn't make a well-formed list, so we can't just
iterate over it. Instead, apply a simple regexp to transform it to a list
which we actually use. Line boundary matching should be enabled.

contrib/hgk

@@ -457,13 +457,11 proc readrefs {} {
         }
     }
 
-    foreach {tag rev} $tags {
+    foreach {- tag rev id} [regexp -inline -all -line {^(.+\S)\s+(\d+):(\S+)} $tags] {
         # we use foreach as Tcl8.4 doesn't support lassign
-        foreach {- id} [split $rev :] {
             lappend tagids($tag) $id
             lappend idtags($id) $tag
         }
-    }
 
     set status [catch {exec $env(HG) --config ui.report_untrusted=false heads} heads]
     if { $status != 0 } {