lib/base: introduce HEIM_BASE_USE_PATH_TOKENS
KRB5_USE_PATH_TOKENS cannot be used within lib/base as its value
is declared in lib/krb5/krb5.h. Declare HEIM_BASE_USE_PATH_TOKENS
in lib/base/baselocl.h and test for it in
heim_config_parse_file_multi().
By conditionalizing heim_config_parse_file_multi() behavior on
KRB5_USE_PATH_TOKENS heim_expand_path_tokens() is not executed
and open() is called on a path without token substitution. As a
result open() always fails with ENOENT.
Change-Id: I29dc018bc560519b76314232b2d51f53bde6313c