More adb buffer fixes.

This patch factors out a lot of the basic protocol code: sending OKAY,
sending FAIL, and sending a length-prefixed string.

ADB_TRACE has been non-optional for a long time, so let's just remove
the #ifs.

Also actually build the device tracker test tool (and remove its duplicate).

Bug: http://b/20666660
Change-Id: I6c7d59f18707bdc62ca69dea45547617f9f31fc6
diff --git a/adb.h b/adb.h
index b8c6156..fd9d0e6 100644
--- a/adb.h
+++ b/adb.h
@@ -209,6 +209,8 @@
     unsigned char token[TOKEN_SIZE];
     fdevent auth_fde;
     unsigned failed_auth_attempts;
+
+    const char* connection_state_name() const;
 };
 
 
@@ -369,7 +371,6 @@
 #define USB_FFS_ADB_IN    USB_FFS_ADB_EP(ep2)
 #endif
 
-int sendfailmsg(int fd, const char *reason);
 int handle_host_request(char *service, transport_type ttype, char* serial, int reply_fd, asocket *s);
 
 void handle_online(atransport *t);