Add get_*architecture() API, extend find_path*() API

* Add get_architecture(), get_primary_architecture(),
get_secondary_architectures(), guess_architecture_for_path() to get
the caller's architecture, the primary architecture, all secondary
architectures, or the architecture associated with a specified path
respectively.
* Rename the find_path*() functions to find_path*_etc() and add an
optional architecture parameter. Add simplified find_path*()
functions.
* BPathFinder: Add FindPath[s]() versions with an architecture
parameter.

Add new API find_path[s](), find_path_for_path()

The new functions are meant to replace many uses of find_directory():
* find_paths() is supposed to be used when the directories of a certain
kind in all installation directories are needed (e.g. font
directories, add-on directory, etc.). Using this API makes code
robust wrt addition or removal of installation locations.
* find_path() is supposed to be used when files/directories associated
with a loaded program, library, or add-on need to be found (e.g. data
files or global settings).
* find_path_for_path() is similar to find_path(), but it starts from a
given path instead of an image.

Add symbol versioning for find_directory()

Should already have been done back when the semantics for the
B_COMMON_*DIRECTORY constants was changed.

Currently old and new version behave the same. So this is just a
contingency measure ATM.

Add get_*architecture() API, extend find_path*() API

* Add get_architecture(), get_primary_architecture(),
get_secondary_architectures(), guess_architecture_for_path() to get
the caller's architecture, the primary architecture, all secondary
architectures, or the architecture associated with a specified path
respectively.
* Rename the find_path*() functions to find_path*_etc() and add an
optional architecture parameter. Add simplified find_path*()
functions.
* BPathFinder: Add FindPath[s]() versions with an architecture
parameter.

Add new API find_path[s](), find_path_for_path()

The new functions are meant to replace many uses of find_directory():
* find_paths() is supposed to be used when the directories of a certain
kind in all installation directories are needed (e.g. font
directories, add-on directory, etc.). Using this API makes code
robust wrt addition or removal of installation locations.
* find_path() is supposed to be used when files/directories associated
with a loaded program, library, or add-on need to be found (e.g. data
files or global settings).
* find_path_for_path() is similar to find_path(), but it starts from a
given path instead of an image.

Add symbol versioning for find_directory()

Should already have been done back when the semantics for the
B_COMMON_*DIRECTORY constants was changed.

Currently old and new version behave the same. So this is just a
contingency measure ATM.