Update Category.php

Create Temporary Table('catalog_category_entity_tmp') if not Exists, after receiving "Error: SQLSTATE[42S01]: Base table or view already exists: 1050 Table 'catalog_category_entity_tmp' already exists", during Category Import.
Merge pull request #1 from danslo/preload-stock

preload stock data
Merge pull request #12 from bragento/master

Preventing Error if $categoryTableTmp already exists