fix #H7156 - perm_invent

Bug report #H7156 listed three items, all relating to perm_invent:
1) it shouldn't persist across save/restore since restore might be
   on a system which doesn't have enough room to display it (report
   actually complained that config file setting was ignored when
   restoring old games, which is an expected side-effect for options
   that persist across save/restore);
2) permanent inventory wasn't updated when using scroll of charging;
3) attempts to update permanent inventory during restore could lead
   to crash if it tries to access shop cost for unpaid items.
Items (2) and (3) have already been fixed.  This fixes (1).

Replace 'flags.perm_invent' with a dummy flag, preserving save files
while removing it from flags.  Add 'iflags.perm_invent' to hold the
value of the perm_invent option.

The win32 files that are updated here haven't been tested.  Whichever
branch contains the curses interface needs to be updated; ditto for
any other pending/potential interfaces which support perm_invent.

doc/Guidebook.mn

@@ -3004,7 +3004,6 @@ such as ``paranoid_confirmation:attack pray Remove''.
 .lp perm_invent
 If true, always display your current inventory in a window.  This only
 makes sense for windowing system interfaces that implement this feature.
-Persistent.
 .lp pettype
 Specify the type of your initial pet, if you are playing a character class
 that uses multiple types of pets; or choose to have no initial pet at all.

doc/Guidebook.tex

@@ -3501,7 +3501,6 @@ such as ``{\it par\-a\-noid\verb+_+con\-fir\-ma\-tion:attack~pray~Remove}''.
 \item[\ib{perm\verb+_+invent}]
 If true, always display your current inventory in a window.  This only
 makes sense for windowing system interfaces that implement this feature.
-Persistent.
 %.lp
 \item[\ib{pettype}]
 Specify the type of your initial pet, if you are playing a character class

doc/fixes36.2

@@ -136,6 +136,8 @@ tty: ensure that current status fields are always copied to prior status
 
 Platform- and/or Interface-Specific Fixes
 -----------------------------------------
+move 'perm_invent' value from flags to iflags to keep it out of save files;
+	affects X11, win32, and curses
 windows-gui: In nethackw, there could be conflicts between menu accelerators 
 	and an extra choice accelerator to fix H7132.
 windows-gui: recognize new BL_RESET in status_update; no change in behavior yet