maint: adjustments to recent timeout change

maint: adjustments to recent timeout change

* .gitignore: Add /lib/fenv.h to ignore list.
* tests/timeout/timeout-parameters.sh: Use a sleep length of 10s
to be consistent with the pattern where we use this larger time
when it does not slow down a test, but also provides protection
against a hung test, and better avoidance of false failures due
to races on very loaded systems.  Also fix the setting of FAIL.
* tests/timeout/timeout-large-parameters.sh: Remove duplicated test.