update macros in yat.m4 to reflect that libyat no longer has a dependency to a cblas lib

[Peter]

Spin-off from #518

Check that they work.

YAT_LA_FILE is incorrect because yat-config --link-libtool now returns /path/to/libyat.la $YAT_BLAS_LIB. The second term is necessary because libyat.la no longer holds information about cblas. Anyway, the variable must be corrected. We probably need to add a another option in yat-config (--yat-la-file) and perhaps we should set a variable in the autoconf macro that reflects the output from --link-libtool (or the user can call $YAT_CONFIG --link-libtool himself).

If we change the behavior of YAT_LA_FILE, the example in doxygen BUILD_TOOLS with YAT_LA_FILE will not work anymore, so that docs need to updated. This will potentially break users builds so it must be mentioned in NEWS.

[Peter]

(In [1893]) remove example that will not work with yat 0.6. refs #525

[Peter]

(In [2020]) adding option yat-la-file in yat-config. refs #525.

[Peter]

(In [2021]) fixes #525 and #518

Added a variable YAT_LT_ADD in YAT_CHECK_LIB. Made YAT_LA_FILE also work with old (0.5) yat-config.

fixed a bug in _YAT_ACTION so $3 is executed and not $2 when appropriate.