Add some missing whitespace/linefeeds in a few manpages.

sys/sys/mutex2: Fix mutex(9) man page

"mtxex" does no exist after cabfc9f6989fa1e4dbccc61162309bd2ec6891c9.

Fix some minor issues in several manual pages.

mutex.9: Adjust for latest changes (ident was moved to mtx_init()).

mutex.9: Adjust a bit to current source.

locking.9 updates

fortune(6)/mutex.9: s/is is/is/

mutex.9: Misc updates and minor improvements.

* mtx_spinlock_ex() and mtx_spinlock_sh() do not exist anymore. mtx_spinlock()
replaced both.

* Add MLINKS for mtx_lock(), mtx_spinlock_try() and mtx

mutex.9: Misc updates and minor improvements.

* mtx_spinlock_ex() and mtx_spinlock_sh() do not exist anymore. mtx_spinlock()
replaced both.

* Add MLINKS for mtx_lock(), mtx_spinlock_try() and mtx_spinunlock().

* Use .Fn for function name mtx_lock_ex_quick().

* Add some text describing mtx_lock(), mtx_spinlock_try() and mtx_spinunlock().

* Start a sentence with capital letter but avoid starting with a function name.

* Add a missing .Fa.

* Add a cross reference to sleep(9) in the SEE ALSO section.

* Bump date.

Reviewed-by: swildner

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manpages: Uniformly order the prologue macros by Dd/Dt/Os.

This is the most widely used order and it also silences warnings
in mandoc -Tlint output.

mutex.9: Adjust .Nm a bit and fix FILES section.

mutex.9: Fix typos in two function names.

Fix some synopses in various manual pages.

mutex.9: Fix typo.

Add a mutex(9) manual page.

Submitted-by: Venkatesh Srinivas <me@endeavour.zapto.org>