hgk: simplify tags parser

As when hg tags is being called without -v option, it returns
lines with two elements in each, we can just interate them as
if it were a usual Tcl list using foreach and two variables.
Line endings and whitespace don't matter when doing so, so we
may keep them as is.

When we're processing the lines, tag variable is assigned a tag
name, and rev is a string in form of revision:hash which we can
split on colon. As Tcl8.4 lacks lassign command, and using lindex
makes code a bit less readable, we use foreach to iterate over
two-element list.

contrib/hgk

@@ -456,16 +456,13 b' proc readrefs {} {'
             exit 2
         }
     }
-    regsub -all "\r\n" $tags "\n" tags
-
-    set lines [split $tags "\n"]
-    foreach f $lines {
-	regexp {(\S+)$} $f full
-	regsub {\s+(\S+)$} $f "" direct
-	set sha [split $full ':']
-	set tag [lindex $sha 1]
-	lappend tagids($direct) $tag
-	lappend idtags($tag) $direct
+
+    foreach {tag rev} $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]