KPath: Use an object_cache for the path buffers in the normal case.

This was (following the packagefs changes) the number-one (by call
count) consumer of malloc() during the boot -- 52866 calls, and 100%
of them either 1024 or 1025 bytes!

Virtually all of these are ephemeral (indeed, the object_cache
stats after a boot with this patch shows there is only a single slab
of 64 buffers allocated, and most of them unused), so this is
probably a significant performance boost.

Change-Id: I659f5707510cbfeafa735d35eea7b92732ead666

headers/private/kernel/fs/KPath.h

@@ -23,14 +23,14 @@ public:
 		LAZY_ALLOC = 0x04
 	};
 public:
-								KPath(size_t bufferSize = B_PATH_NAME_LENGTH);
+								KPath(size_t bufferSize = B_PATH_NAME_LENGTH + 1);
 								KPath(const char* path, int32 flags = DEFAULT,
-									size_t bufferSize = B_PATH_NAME_LENGTH);
+									size_t bufferSize = B_PATH_NAME_LENGTH + 1);
 								KPath(const KPath& other);
 								~KPath();
 
 			status_t			SetTo(const char* path, int32 flags = DEFAULT,
-									size_t bufferSize = B_PATH_NAME_LENGTH);
+									size_t bufferSize = B_PATH_NAME_LENGTH + 1);
 			void				Adopt(KPath& other);
 
 			status_t			InitCheck() const;
@@ -67,6 +67,7 @@ public:
 
 private:
 			status_t			_AllocateBuffer();
+			void				_FreeBuffer();
 			status_t			_Normalize(const char* path,
 									bool traverseLeafLink);
 			void				_ChopTrailingSlashes();