Improve STL representation detection

Previously, the STL loader relied on a string check at the start of the
buffer to determine if the STL file was of ASCII representation.  This led to
certain false-positives for binary STL files with the magic string present in
their header.  This patch addresses the issue by adding a proper binary check
to the representation detection.
Merge pull request #79 from jdduke/stl_binary_check

Improve STL representation detection
Fix Android compilation with STLport

Satisfy STLport's runtime_error constructor with an explicit string argument.
Merge pull request #81 from jdduke/android_fix

Fix Android compilation with STLport
Update Readme.md
add missing <sstream> header to lexical_cast replacement
fix error "Chunk is too large" with gcc >=4.7.0 / mingw64
Merge pull request #83 from abma/master

fix .3DS error "Chunk is too large" with gcc >=4.7.0 / mingw
Add aiFreeScene() API for symmetry with aiCopyScene.
Clarify exporter doc: how to get a modifiable copy of a previously imported scene.
Merge branch 'master' of github.com:assimp/assimp
CMake for assimp_view: copy dlls from assimp build over to output folder.
CMake for assimp_cmd: also copy over assimp output binary as PRE_BUILD event.
CMake: use copy_if_different instead of copy and only run PRE_BUILD on Windows as it is not required on *nix anyway.
LWO: ignore chunks of length zero.
LWO: take last CLIP with the requested index (CLIPs ordered by ordinal string)
Merge pull request #89 from assimp/cmake-fixes

CMake Fixes
Merge branch 'master' of github.com:assimp/assimp into fixes
CMake: simplify.
CMake: make assimp_view/assimp_cmd's file copying DEPEND on assimp.