libarchive: FEATURE_LZMA_FAST should be visible if FEATURE_SEAMLESS_LZMA

While at it, tweak some config help texts.

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

editors/vi.c

@@ -61,7 +61,7 @@
 //config:	default y
 //config:	depends on VI
 //config:	help
-//config:	  This will enable you to use yank and put, as well as mark.
+//config:	  This enables you to use yank and put, as well as mark.
 //config:
 //config:config FEATURE_VI_SEARCH
 //config:	bool "Enable search and replace cmds"