libsparse: rename symbols that conflict with libext4_utils

Until ext4_utils switches to using libsparse, libext4_utils defines some
of the same symbols as libsparse.  Fastboot links statically against
both of them, and there is no easy way to make the symbols hidden, so
just rename them in libsparse.

Change-Id: Idc2cfe20efe3c3a7fb8233f453a89bbbeb0dcc8b