The otp_src_R13B02_OTP-8199.patch fixes the following issue present
in otp_src_R13B02:

OTP-8199 In the new release of Reltool (0.5) there is a severe bug
         that may cause your source files to be deleted. The bug is
         triggered when you generate a target system WITH archive
         files AND your library directories are given with absolute
         paths. (Library directories are given with the ERL_LIBS
         environment variable or with the lib_dirs configuration
         parameter.)

You need to apply the patch with a gnu patch compatible patch program.

How to apply the patch:
  $ ls
  otp_src_R13B02_OTP-8199.patch  otp_src_R13B02.tar.gz
  $ gtar -zxf otp_src_R13B02.tar.gz 
  $ patch -ZNp0 < otp_src_R13B02_OTP-8199.patch
  patching file otp_src_R13B02/lib/reltool/src/reltool_target.erl
  $ cd otp_src_R13B02
  $ # configure, make, and make install as usual...