title: have trouble in installing biopython package
body: <p>im using mac 10.6.7, and xcode 4 with gcc 4.2 installed.
  but when i was installing biopython with:
      python setup.py install
  on the command, it gives out error on gcc:</p>
  
  <pre><code>10-54-41-155-wireless1x:biopython-1.57 xueran2010$ python setup.py install
  running install
  running build
  running build_py
  running build_ext
  building 'Bio.cpairwise2' extension
  gcc-4.2 -fno-strict-aliasing -fno-common -dynamic -DNDEBUG -g -fwrapv -Os -Wall -Wstrict-prototypes -DENABLE_DTRACE -arch i386 -arch ppc -arch x86_64 -pipe -IBio -I/System/Library/Frameworks/Python.framework/Versions/2.6/include/python2.6 -c Bio/cpairwise2module.c -o build/temp.macosx-10.6-universal-2.6/Bio/cpairwise2module.o
  /usr/libexec/gcc/powerpc-apple-darwin10/4.2.1/as: assembler         (/usr/bin/../libexec/gcc/darwin/ppc/as or /usr/bin/../local/libexec/gcc/darwin/ppc/as) for architecture ppc not installed
  Installed assemblers are:
  /usr/bin/../libexec/gcc/darwin/x86_64/as for architecture x86_64
  /usr/bin/../libexec/gcc/darwin/i386/as for architecture i386
  Bio/cpairwise2module.c:639: fatal error: error writing to -: Broken pipe
  compilation terminated.
  lipo: can't open input file: /var/folders/ir/ir6RCJTKGB4QU5sVdTXwt++++TI/-Tmp-//cccUvTiF.out (No such file or directory)
  error: command 'gcc-4.2' failed with exit status 1
  </code></pre>