Fix compile error on gcc 4.7

Many std headers included <unistd.h> by default.
This has been changed in gcc 4.7, and <unistd.h> is no longer included,
which causes `* was not declared' errors.
Including <unistd.h> manually fixes this problem.

git-svn-id: svn+ssh://cvs.lpds.sztaki.hu/var/lib/svn/szdg/dcapi/trunk@2601 a7169a2c-3604-0410-bc95-c702d8d87f7a

dcapi/boinc/client.C

@@ -16,6 +16,7 @@
 #include <string.h>
 #include <limits.h>
 #include <stdio.h>
+#include <unistd.h>
 
 #ifndef _WIN32
 #include <dirent.h>