Remélem, édesanyjuk csuklik ilyenkor:

Apache Serf uses SCons 2.3 for its build system. If it is not installed
on your system, then you can install it onto your system. 
To build serf:
 
$ scons APR=/path/to/apr APU=/path/to/apu OPENSSL=/openssl/base PREFIX=/path/to/prefix