Minor optimization for strlen and memcpy calls for reading blend files

Summary:
This commit removes ~10000 strlen calls and ~100000 memcpy calls in blender (profiled with blender --background), ~10000 memcpy calls in makesdna.

There is no need to create null-terminated strings for atoi, because it converts only the initial portion of the string anyway.
Also it was noticed that DNA_elem_array_size and arraysize functions work only with full strings, so there is no point to calculate strlen.

Reviewers: campbellbarton

Reviewed By: campbellbarton

Differential Revision: http://developer.blender.org/D105
Editmesh: skip allocating a face array for recalc-normals
Fix typo in previous own commit (thanks to _FrnchFrgg_ for noticing this!).
Merge branch 'master' of http://git.blender.org/blender