*: kill bb_get_last_path_component, replace with two functions

(one which strips trailing slash and one which does not)
wget: straighten out as a result of above change
   text    data     bss     dec     hex filename
   5056       1       0    5057    13c1 busybox.t4/networking/wget.o
   5022       0       0    5022    139e busybox.t5/networking/wget.o

libbb/get_last_path_component.c

@@ -8,25 +8,35 @@
  */
 
 #include "libbb.h"
-
-char *bb_get_last_path_component(char *path)
+/*
+ * "/"        -> "/"
+ * "abc"      -> "abc"
+ * "abc/def"  -> "def"
+ * "abc/def/" -> ""
+ */
+char *bb_get_last_path_component_nostrip(const char *path)
 {
-	char *first = path;
-	char *last;
+	char *slash = strrchr(path, '/');
 
-	last = path - 1;
+	if (!slash || (slash == path && !slash[1]))
+		return (char*)path;
 
-	while (*path) {
-		if ((*path != '/') && (path > ++last)) {
-			last = first = path;
-		}
-		++path;
-	}
-
-	if (*first == '/') {
-		last = first;
-	}
-	last[1] = '\0';
-
-	return first;
+	return slash + 1;
+}
+
+/*
+ * "/"        -> "/"
+ * "abc"      -> "abc"
+ * "abc/def"  -> "def"
+ * "abc/def/" -> "def" !!
+ */
+char *bb_get_last_path_component_strip(char *path)
+{
+	char *slash = last_char_is(path, '/');
+
+	if (slash)
+		while (*slash == '/' && slash != path)
+			*slash-- = '\0';
+
+	return bb_get_last_path_component_nostrip(path);
 }

libbb/run_shell.c

@@ -67,7 +67,7 @@ void run_shell(const char *shell, int loginshell, const char *command, const cha
 
 	args = xmalloc(sizeof(char*) * (4 + additional_args_cnt));
 
-	args[0] = bb_get_last_path_component(xstrdup(shell));
+	args[0] = bb_get_last_path_component_nostrip(xstrdup(shell));
 
 	if (loginshell)
 		args[0] = xasprintf("-%s", args[0]);