Let 'make install' clear all cachefiles

Signed-off-by: Lars Hjemli <hjemli@gmail.com>

Makefile

@@ -2,6 +2,7 @@ CGIT_VERSION = 0.1-pre
 
 INSTALL_BIN = /var/www/htdocs/cgit.cgi
 INSTALL_CSS = /var/www/htdocs/cgit.css
+CACHE_ROOT = /var/cache/cgit
 
 EXTLIBS = ../git/libgit.a ../git/xdiff/lib.a -lz -lcrypto
 OBJECTS = config.o html.o cache.o
@@ -13,6 +14,7 @@ all: cgit
 install: all
 	install cgit $(INSTALL_BIN)
 	install cgit.css $(INSTALL_CSS)
+	rm -rf $(CACHE_ROOT)/*
 
 cgit: cgit.c cgit.h git.h $(OBJECTS)
 	$(CC) $(CFLAGS) -DCGIT_VERSION='"$(CGIT_VERSION)"' cgit.c -o cgit $(OBJECTS) $(EXTLIBS)