simplize server tools
当path为空的时候就会报错，跑不下去了

path为空的场景是将seajs源码以内联形式输出输出的时候，其script的src属性为""。
跑到这里的时候便会报错
https://github.com/seajs/seajs/blob/master/src/util-path.js#L176

增强dirname的容错性
dirname add empty string test
Fix a bug in plugin-shim. close #694
Merge branch 'master' of github.com:seajs/seajs
Merge pull request #692 from siemenliu/patch-1

dirname函数 当path=""时报错
Update version to 2.0.1
Make sure that the input to dirname() is not empty value
Rebuild packages
Tweak code style
Fix a bug due to compression. fix #710
Fix a bug for shim plugin when src is equal to key. fix #706
Improve getUnloadedUris speed
Revert code of plugin shim
Update version to 2.1.0
Remove circular dependencies support
Comments specs for circular dependencies
Comments specs for circular dependencies
Rebuild packages
Remove async loading support for sea.js self. close #733