proc,service,terminal: information about stack trace truncation

Add a flag to Stackframe that indicates where the stack frame is the
bottom-most frame of the stack. This allows clients to know whether the
stack trace terminated normally or if it was truncated because the
maximum depth was reached.
Add a truncation message to the 'stack' command.

service/api/types.go

@@ -131,6 +131,8 @@ type Stackframe struct {
 
 	Defers []Defer
 
+	Bottom bool `json:"Bottom,omitempty"` // Bottom is true if this is the bottom frame of the stack
+
 	Err string
 }