manpage: remove bugs which are fixed

manpage: remove bugs which are fixed

"A traced process ignores SIGSTOP" - fixed, expected to be in linux-3.4.x.
"A traced process which tries to block SIGTRAP will be sent a SIGSTOP
in an attempt to force continuation of tracing." - not needed
and no longer done.
"On Linux, exciting as it would be, tracing the init process is forbidden"
- not true anymore.
"When a traced process receives a SIGTRAP signal not
associated with tracing, strace will not report that signal correctly."
- not true anymore.

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>