tests: few tweakings and cosmetic changes

tests: few tweakings and cosmetic changes

* tests/dist-formats.tap: Fix botched spacing.
* tests/subobjname.test: Prefer spaces to tabs in indentation.
* tests/cond43.test: Likewise.
* tests/comment7.test: Likewise.
* tests/compile_f90_c_cxx.test: Use "$tab" instead of literal
tab characters in the grep regexp.
* tests/compile_f_c_cxx.test: Likewise.
* tests/pluseq3.test: Likewise.
* tests/cond-basic.test: Likewise.
* tests/acloca16.test: Add empty line before trailing ':' command.
* tests/bsource.test: Likewise.
* tests/depend5.test: Likewise.
* tests/depend6.test: Likewise.
* tests/destdir.test: Likewise.
* tests/fort2.test: Likewise.
* tests/instdir-java.test: Likewise.
* tests/instdir-lisp.test: Likewise.
* tests/instdir-python.test: Likewise.
* tests/instdir.test: Likewise.
* tests/instdir2.test: Likewise.
* tests/ltinstloc.test: Likewise.
* tests/missing.test: Likewise.
* tests/missing2.test: Likewise.
* tests/nodef.test: Likewise.
* tests/nodef2.test: Likewise.
* tests/subst4.test: Likewise.
* tests/werror3.test: Likewise.
* tests/commen11.test: Likewise.  Also, make grepping of automake
stderr slightly stricter, and properly quote strings with shell
metacharacters.
* tests/nodep2.test: Add empty line before trailing ':' command.
Do not create unneeded dummy source files.