gitk: Rename 'tagcontents' to 'cached_tagcontent'

Name the 'tagcontents' variable similarly to the rest of the
variables cleared in the changedrefs() function.

This makes the naming consistent and provides a hint that it
should be cleared when reloading gitk's cache.
Suggested-by: NJunio C Hamano <gitster@pobox.com>
Signed-off-by: NDavid Aguilar <davvid@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

gitk

@@ -10599,7 +10599,7 @@ proc movedhead {hid head} {
 }
 
 proc changedrefs {} {
-    global cached_dheads cached_dtags cached_atags tagcontents
+    global cached_dheads cached_dtags cached_atags cached_tagcontent
     global arctags archeads arcnos arcout idheads idtags
 
     foreach id [concat [array names idheads] [array names idtags]] {
@@ -10611,7 +10611,7 @@ proc changedrefs {} {
 	    }
 	}
     }
-    catch {unset tagcontents}
+    catch {unset cached_tagcontent}
     catch {unset cached_dtags}
     catch {unset cached_atags}
     catch {unset cached_dheads}
@@ -10664,7 +10664,7 @@ proc listrefs {id} {
 }
 
 proc showtag {tag isnew} {
-    global ctext tagcontents tagids linknum tagobjid
+    global ctext cached_tagcontent tagids linknum tagobjid
 
     if {$isnew} {
 	addtohistory [list showtag $tag 0] savectextpos
@@ -10673,13 +10673,13 @@ proc showtag {tag isnew} {
     clear_ctext
     settabs 0
     set linknum 0
-    if {![info exists tagcontents($tag)]} {
+    if {![info exists cached_tagcontent($tag)]} {
 	catch {
-           set tagcontents($tag) [exec git cat-file tag $tag]
+           set cached_tagcontent($tag) [exec git cat-file tag $tag]
 	}
     }
-    if {[info exists tagcontents($tag)]} {
-	set text $tagcontents($tag)
+    if {[info exists cached_tagcontent($tag)]} {
+	set text $cached_tagcontent($tag)
     } else {
 	set text "[mc "Tag"]: $tag\n[mc "Id"]:  $tagids($tag)"
     }