closes gh-24 (back-ported from regression fix for tcl-core [2c237beff…

…bace823]):

  - usage of time zones `Etc/GMT±n` is allowed now (were impossible previously due to incorrect prevention of path escape for the tzdata directory);
  - test coverage (test clock-59.2)

lib/clock.tcl

@@ -1222,7 +1222,7 @@ proc ::tcl::clock::LoadTimeZoneFile { fileName } {
     # is security sensitive.  Make sure that the path name cannot escape the
     # given directory.
 
-    if { ![regexp {^[[.-.][:alpha:]_]+(?:/[[.-.][:alpha:]_]+)*$} $fileName] } {
+    if { [regexp {^[/\\]|^[a-zA-Z]+:|(?:^|[/\\])\.\.} $fileName] } {
 	return -code error \
 	    -errorcode [list CLOCK badTimeZone $:fileName] \
 	    "time zone \":$fileName\" not valid"
@@ -1262,7 +1262,7 @@ proc ::tcl::clock::LoadZoneinfoFile { fileName } {
     # is security sensitive.  Make sure that the path name cannot escape the
     # given directory.
 
-    if { ![regexp {^[[.-.][:alpha:]_]+(?:/[[.-.][:alpha:]_]+)*$} $fileName] } {
+    if { [regexp {^[/\\]|^[a-zA-Z]+:|(?:^|[/\\])\.\.} $fileName] } {
 	return -code error \
 	    -errorcode [list CLOCK badTimeZone $:fileName] \
 	    "time zone \":$fileName\" not valid"

tests/clock.test

@@ -38201,6 +38201,23 @@ test clock-59.1 {military time zones} {
     join $trouble \n
 } {}
 
+test clock-59.2 {correct time zone names, format and scan back, bug and regression [2c237beffbace823]} {
+    set result {}
+    foreach {base tz} {
+	 1700000000 "Etc/GMT-2"
+	 1700000000 "Etc/GMT+2"
+	 1301184000 "Europe/Kaliningrad"
+	  152632800 "Pacific/Chatham"
+	 -765317964 "America/Paramaribo"
+	-2337928528 "Australia/Eucla"
+    } {
+	set v [clock format $base -timezone Etc/GMT-2 -format "%Y-%m-%d %H:%M:%S %Z"]
+	lappend result [expr {[set t [clock scan $v -format "%Y-%m-%d %H:%M:%S %Z"]] == $base ? 1 : "0 ($t != $base for $v)"}]
+	lappend result [expr {[set t [clock scan $v]] == $base ? 1 : "0 ($t != $base for $v)"}]
+    }
+    set result
+} [lrepeat 12 1]
+
 # case-insensitive matching of weekday and month names [Bug 1781282]
 
 test clock-60.1 {case insensitive weekday names} {