Use macros IS_IN_SYS(ENTER|EXIT) instead of testing tracee->status directly.
ptrace: Fix (2/2) support for legacy execve notification (a SIGTRAP event).

Send an actual SIGTRAP signal instead of re-using another event slot:

    If the PTRACE_O_TRACEEXEC option is *not* in effect for the
    execing tracee, the kernel delivers an extra SIGTRAP to the tracee
    after execve(2) *returns*.  This is an ordinary signal (similar to
    one which can be generated by "kill -TRAP"), not a special kind of
    ptrace-stop.  Employing PTRACE_GETSIGINFO for this signal returns
    si_code set to 0 (SI_USER).  This signal may be blocked by signal
    mask, and thus may be delivered (much) later.

    -- man 2 ptrace
ptrace: Consider tracee's ptrace options only if it has a ptracer.

These options are not cleared when the ptracee is detached from its
ptracer.

Detected-with: gdb-7.5/gdb/testsuite/gdb.base/multi-forks.exp
ptrace: Restarting signal from ptracer overrides restarting signal from PRoot.

Detected-with: gdb-7.5/gdb/testsuite/gdb.base/condbreak.exp
ptrace: Initial support for the ATTACH request.

Tested-with: gdb-7.5/gdb/testsuite/gdb.base/*attach*.exp
ptrace: Don't rely on tracee->parent to know if the inheritance has failed.

This field is set to NULL when the parent dies before its children.
Use tracee->exe instead.

Detected-with: gdb-7.5/gdb/testsuite/gdb.base/multi-forks.exp
ptrace: Initial support for {G,S}ETFPREGS 32-bit request on 64-bit.

This support is almost empty, although it makes the GDB testsuite go
further when using a 32-bit guest on a 64-bit host.
ptrace: Fix "struct user.u_debugreg" 32-bit/64-bit offsets conversion.

Detected-with: gdb-7.5/gdb/testsuite/gdb.base/info-os.exp
ptrace: Warn when a user area 32/64-bit conversion is not yet supported.
ptrace: Initial support for {G,S}ET_THREAD_AREA 32-bit request on 64-bit.

Tested-with: gdb-7.5/gdb/testsuite/gdb.base/info-os.exp
ptrace: Add support for SINGLEBLOCK request.

Tested-with: utrace/ptrace-tests/tests/block-step
ptrace: Always report WIFEXITED and WIFSIGNALED events to the ptracer.

Detected-with: ltp-full-20140422/testcases/kernel/syscalls/ptrace/ptrace0{3,5}