Basic Alembic support

All in all, this patch adds an Alembic importer, an Alembic exporter,
and a new CacheFile data block which, for now, wraps around an Alembic
archive. This data block is made available through a new modifier ("Mesh
Sequence Cache") as well as a new constraint ("Transform Cache") to
somewhat properly support respectively geometric and transformation data
streaming from alembic caches.

A more in-depth documentation is to be found on the wiki, as well as a
 guide to compile alembic: https://wiki.blender.org/index.php/
User:Kevindietrich/AlembicBasicIo.

Many thanks to everyone involved in this little project, and huge shout
out to "cgstrive" for the thorough testings with Maya, 3ds Max, Houdini
and Realflow as well as @fjuhec, @jensverwiebe and @jasperge for the
custom builds and compile fixes.

Reviewers: sergey, campbellbarton, mont29

Reviewed By: sergey, campbellbarton, mont29

Differential Revision: https://developer.blender.org/D2060

source/blender/python/intern/bpy_app_build_options.c

@@ -69,6 +69,7 @@ static PyStructSequence_Field app_builtopts_info_fields[] = {
 	{(char *)"player", NULL},
 	{(char *)"openmp", NULL},
 	{(char *)"openvdb", NULL},
+	{(char *)"alembic", NULL},
 	{NULL}
 };
 
@@ -303,6 +304,12 @@ static PyObject *make_builtopts_info(void)
 	SetObjIncref(Py_False);
 #endif
 
+#ifdef WITH_ALEMBIC
+	SetObjIncref(Py_True);
+#else
+	SetObjIncref(Py_False);
+#endif
+
 #undef SetObjIncref
 
 	return builtopts_info;