Escape python code to fix python 3.3 build issue on Mac

Turns out that len is an m4 macro.

configure.ac

@@ -47,8 +47,7 @@ if [[ "$PYTHON_EXEC_PREFIX" != "$PYTHON_PREFIX" ]]; then
   ADD_PYTHON_LIBDIR([${PYTHON_EXEC_PREFIX}/lib/python${PYTHON_VERSION}/config/])
   ADD_PYTHON_LIBDIR([${PYTHON_EXEC_PREFIX}/lib/python${PYTHON_VERSION}/config-${PYTHON_VERSION}${PYTHON_ABIFLAGS}/])
 fi
-PYTHON_LIBS=$($PYTHON -c "import sys
-result = None
+PYTHON_LIBS=$($PYTHON -c ["result = None
 try:
   import sysconfig
   lib = sysconfig.get_config_var('PY3LIBRARY')
@@ -59,7 +58,7 @@ except:
 if result is None:
   result = '-lpython${PYTHON_VERSION}${PYTHON_ABIFLAGS}'
 print(result)
-")
+"])
 
 AC_SUBST(PYTHON_CFLAGS)
 AC_SUBST(PYTHON_LDFLAGS)