Log Message:
textproc/libxls: Update to 1.6.1

Changes in 1.6.0:

 - This release enables decoding of non-Unicode character sets in older
   (BIFF5) XLS files. In addition, it improves string-conversion
   performance in newer files.

   See: https://github.com/libxls/libxls/pull/77

Changes in 1.6.1:

 - This release corrects the libtool version information found in libxls
   1.6.0, and fixes undefined behavior for applications that were
   originally linked against the 1.5.x dynamic library. The C source
   code is unchanged from the last release.

   See: https://github.com/libxls/libxls/issues/79