patch 8.1.2082: some files have a weird name to fit in 8.3 characters

Problem:    Some files have a weird name to fit in 8.3 characters.
Solution:   Use a nicer names.
diff --git a/src/Makefile b/src/Makefile
index 0f949a8..75085ee 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -1638,7 +1638,7 @@
 	optionstr.c \
 	os_unix.c \
 	auto/pathdef.c \
-	popupmnu.c \
+	popupmenu.c \
 	popupwin.c \
 	profiler.c \
 	pty.c \
@@ -1774,7 +1774,7 @@
 	objects/optionstr.o \
 	objects/os_unix.o \
 	objects/pathdef.o \
-	objects/popupmnu.o \
+	objects/popupmenu.o \
 	objects/popupwin.o \
 	objects/profiler.o \
 	objects/pty.o \
@@ -1935,7 +1935,7 @@
 	optionstr.pro \
 	os_mac_conv.pro \
 	os_unix.pro \
-	popupmnu.pro \
+	popupmenu.pro \
 	popupwin.pro \
 	profiler.pro \
 	pty.pro \
@@ -3341,8 +3341,8 @@
 objects/pathdef.o: auto/pathdef.c
 	$(CCC) -o $@ auto/pathdef.c
 
-objects/popupmnu.o: popupmnu.c
-	$(CCC) -o $@ popupmnu.c
+objects/popupmenu.o: popupmenu.c
+	$(CCC) -o $@ popupmenu.c
 
 objects/popupwin.o: popupwin.c
 	$(CCC) -o $@ popupwin.c
@@ -3823,7 +3823,7 @@
  os_unix.h auto/osdef.h ascii.h keymap.h term.h macros.h option.h beval.h \
  proto/gui_beval.pro structs.h regexp.h gui.h alloc.h ex_cmds.h spell.h \
  proto.h globals.h
-objects/popupmnu.o: popupmnu.c vim.h protodef.h auto/config.h feature.h os_unix.h \
+objects/popupmenu.o: popupmenu.c vim.h protodef.h auto/config.h feature.h os_unix.h \
  auto/osdef.h ascii.h keymap.h term.h macros.h option.h beval.h \
  proto/gui_beval.pro structs.h regexp.h gui.h alloc.h ex_cmds.h spell.h \
  proto.h globals.h