dialplan: Add test coverage for new variable functions.

This change adds test coverage for the following new dialplan
functions:

GLOBAL_DELETE (deletes a global variable)
DELETE (delets a channel variable)
GLOBAL_EXISTS (checks whether a global variable is set or not)
VARIABLE_EXISTS (checks whether a channel variable is set or not)

tests/pbx/dialplan/configs/ast1/extensions.conf

@@ -67,6 +67,7 @@ exten => start,1,NoOp()
 	same => n,ExecIf($[${TestCounter} = 12]?Goto(base64,start,1))
 	same => n,ExecIf($[${TestCounter} = 13]?Goto(aes,start,1))
 	same => n,ExecIf($[${TestCounter} = 14]?Goto(len,start,1))
+	same => n,ExecIf($[${TestCounter} = 31]?Goto(variable_deletion,start,1))
 
 	; GoSub testing
 	same => n,ExecIf($[${TestCounter} = 24]?Goto(gosubtest,start,1))
@@ -271,6 +272,31 @@ exten => start,1,NoOp()
 	same => n,GotoIf($[${Result} = Fail]?test,result_fail,1)
 	same => n,Goto(test,start,top)
 
+; ------------------------------------------------------------------
+; VARIABLE DELETION (GLOBAL_DELETE, DELETE)
+; ------------------------------------------------------------------
+[variable_deletion]
+exten => start,1,NoOp()
+	same => n,Set(GLOBAL(alice)=exists)
+	same => n,Set(Result=${IF($["${GLOBAL_EXISTS(alice)}" = "1"]?OK:Fail)})
+	same => n,GotoIf($[${Result} = Fail]?test,result_fail,1)
+	same => n,Set(GLOBAL(alice)=)
+	same => n,Set(Result=${IF($["${GLOBAL_EXISTS(alice)}" = "1"]?OK:Fail)})
+	same => n,GotoIf($[${Result} = Fail]?test,result_fail,1)
+	same => n,Set(GLOBAL_DELETE(alice)=)
+	same => n,Set(Result=${IF($["${GLOBAL_EXISTS(alice)}" = "0"]?OK:Fail)})
+	same => n,GotoIf($[${Result} = Fail]?test,result_fail,1)
+	same => n,Set(bob=exists)
+	same => n,Set(Result=${IF($["${VARIABLE_EXISTS(bob)}" = "1"]?OK:Fail)})
+	same => n,GotoIf($[${Result} = Fail]?test,result_fail,1)
+	same => n,Set(bob=)
+	same => n,Set(Result=${IF($["${VARIABLE_EXISTS(bob)}" = "1"]?OK:Fail)})
+	same => n,GotoIf($[${Result} = Fail]?test,result_fail,1)
+	same => n,Set(DELETE(bob)=)
+	same => n,Set(Result=${IF($["${VARIABLE_EXISTS(bob)}" = "0"]?OK:Fail)})
+	same => n,GotoIf($[${Result} = Fail]?test,result_fail,1)
+	same => n,Goto(test,start,top)
+
 ; ------------------------------------------------------------------
 ; GoSub, Return, LOCAL, LOCAL_PEEK
 ; ------------------------------------------------------------------