tests: more meaningful names for some test cases

tests: more meaningful names for some test cases

* t/yacc5.sh: Renamed ...
* t/yacc-grepping2.sh: ... like this.
* t/yacc7.sh: Renamed ...
* t/yacc-headers-and-pr47.sh: ... like this.
* t/yacc8.sh: Renamed ...
* t/yacc-subdir.sh: ... like this.
* t/subdir10.sh: Rename ...
* t/subdir-env-interference.sh: ... like this.
* t/specflg10.sh: Rename ...
* t/am-default-source-ext.sh: ... like this.
* t/suffix12.sh: Rename ...
* t/suffix-custom-subobj.sh: ... like this.
* t/suffix13.sh: Rename ...
* t/suffix-custom-subobj-and-specflg.sh: ... like this.
* t/check3.sh: Rename ...
* t/built-sources-check.sh: ... like this.
* t/subdirbuiltsources.sh: Rename ...
* t/built-sources-subdir.sh: ... like this.
* t/bsource.sh: Rename ...
* t/no-spurious-install-recursive.sh: ... like this.
* t/list-of-tests.mk: Adjust.

Signed-off-by: Stefano Lattarini <stefano.lattarini@gmail.com>