[Server] Utils: Optimize getSelfExeDir() by using memchr().

Use memrchr() to find path separator '/'.

Signed-off-by: YOSHIFUJI Hideaki <hideaki.yoshifuji@miraclelinux.com>
Merge pull request #346 from project-hatohol/server-utils-optimization-20140807

[Server] Utils: Optimize getSelfExeDir() by using memchr().