tweaks: harmonize some prototypes with their functions

Match three variable names in the prototypes
to the changd ones in their functions in utils.c.

src/proto.h

@@ -601,9 +601,9 @@ char *mallocstrcpy(char *dest, const char *src);
 char *free_and_assign(char *dest, char *src);
 size_t get_page_start(size_t column);
 size_t xplustabs(void);
-size_t actual_x(const char *s, size_t column);
-size_t strnlenpt(const char *s, size_t maxlen);
-size_t strlenpt(const char *s);
+size_t actual_x(const char *text, size_t column);
+size_t strnlenpt(const char *text, size_t maxlen);
+size_t strlenpt(const char *text);
 void new_magicline(void);
 #if !defined(NANO_TINY) || defined(ENABLE_HELP)
 void remove_magicline(void);