man: Misc syntax fixes

- loader.efi.8: use proper way of printing a backslash.
- usr.bin/gzip/gzip.1: contained a non-breaking space (in utf-8, 0xC2A0).
- lib/libpmc/pmc.*.3: remove two duplicate .Xr lines

Signed-off-by:	Graham Percival <gperciva@tarsnap.com>
Reviewed by:	mhorne, Alexander Ziaee <concussious.bugzilla@runbox.com>
MFC after:	3 days
Sponsored by:	Tarsnap Backup Inc.
Pull Request:	https://github.com/freebsd/freebsd-src/pull/1523

lib/libpmc/pmc.cmn-600.3

@@ -560,7 +560,6 @@ Average latency to form a TX TLP
 .Xr pmc.corei7 3 ,
 .Xr pmc.corei7uc 3 ,
 .Xr pmc.iaf 3 ,
-.Xr pmc.iaf 3 ,
 .Xr pmc.soft 3 ,
 .Xr pmc.tsc 3 ,
 .Xr pmc.westmere 3 ,

lib/libpmc/pmc.dmc-620.3

@@ -130,7 +130,6 @@ The following PMC events are available:
 .Xr pmc.corei7 3 ,
 .Xr pmc.corei7uc 3 ,
 .Xr pmc.iaf 3 ,
-.Xr pmc.iaf 3 ,
 .Xr pmc.soft 3 ,
 .Xr pmc.tsc 3 ,
 .Xr pmc.westmere 3 ,

stand/man/loader.efi.8

@@ -394,7 +394,7 @@ BootCurrent: 0001
 Timeout    : 2 seconds
 BootOrder  : 0000, 0001, 0003, 0004, 0005, 0006, 0001, 0008, 000A, 000B, 000C, 000E, 0007
 \&...
-+Boot0001* FreeBSD ZPOOL HD(1,GPT,b5d0f86b-265d-1e1b-18aa-0ed55e1e73bd,0x28,0x96000)/File(\EFI\FREEBSD\LOADER.EFI)
++Boot0001* FreeBSD ZPOOL HD(1,GPT,b5d0f86b-265d-1e1b-18aa-0ed55e1e73bd,0x28,0x96000)/File(\eEFI\eFREEBSD\eLOADER.EFI)
                             nda0p1:/EFI/FREEBSD/LOADER.EFI /boot/efi//EFI/FREEBSD/LOADER.EFI
 \&...
 .Ed

usr.bin/gzip/gzip.1

@@ -189,7 +189,7 @@ Options on the command line will override anything in
 .Sh EXIT STATUS
 The
 .Nm
-utility exits 0 on success,
+utility exits 0 on success,
 1 on errors,
 and 2 if a warning occurs.
 .Sh SIGNALS