testbot/testagentd: Only rebuild the iso file if the Windows binary has changed.

[Francois Gouget]

But always recreate the winetest directory from scratch in case it was left from a previous failed build.
---
 testbot/src/testagentd/Makefile |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/testbot/src/testagentd/Makefile b/testbot/src/testagentd/Makefile
index 6090d02..f6035be 100644
--- a/testbot/src/testagentd/Makefile
+++ b/testbot/src/testagentd/Makefile
@@ -27,7 +27,10 @@ TestAgentd.exe: testagentd.obj platform_windows.obj
 C_SRCS = testagentd.c platform_unix.c platform_windows.c
 $(C_SRCS:.c=.o) $(C_SRCS:.c=.obj): platform.h
 
-iso: windows
+iso: winetestbot.iso
+
+winetestbot.iso: TestAgentd.exe
+	rm -rf winetest
 	mkdir winetest
 	cp TestAgentd.exe winetest
 	mkisofs="mkisofs"; \
-- 
1.7.10.4