Log Message:
net/libfetch: Fix for gcc4.7

When building with gcc4.7, libfetch fails with the following error:
  ftp.c: In function 'unmappedaddr':
  ftp.c:149:2: error: dereferencing type-punned pointer will break
               strict-aliasing rules [-Werror=strict-aliasing]
  cc1: all warnings being treated as errors
  *** Error code 1

The code is intentionally grouping an array of four uint8_t bytes into a
uint32_t word.  Add -Wno-strict-aliasing in makefile to fix build in gcc4.7.