Fix multi-threading issue
Fix multi-threading issue

yara_callback was invoking Python's code without acquiring the global interpreter lock.

plusvic/yara-python,grrrrrrrrr/yara-python,VirusTotal/yara-python,plusvic/yara-python,wxsBSD/yara-python,VirusTotal/yara-python,wxsBSD/yara-python,grrrrrrrrr/yara-python