Fix calculation of tag count in dotclear import
Fix calculation of tag count in dotclear import

Upon import of a dotclear backup, `pelican-import` returned this stacktrace:

```
  File "/usr/bin/pelican-import", line 11, in <module>
    sys.exit(main())
  File "/usr/lib/python3.4/site-packages/pelican/tools/pelican_import.py", line 809, in main
    attachments = attachments or None)
  File "/usr/lib/python3.4/site-packages/pelican/tools/pelican_import.py", line 621, in fields2pelican
    kind, in_markup) in fields:
  File "/usr/lib/python3.4/site-packages/pelican/tools/pelican_import.py", line 262, in dc2fields
    if int(tag[:1]) == 1:
ValueError: invalid literal for int() with base 10: 'a'
```
karlcow/pelican,ls2uper/pelican,number5/pelican,ingwinlu/pelican,Rogdham/pelican,talha131/pelican,douglaskastle/pelican,catdog2/pelican,gymglish/pelican,avaris/pelican,jimperio/pelican,Scheirle/pelican,JeremyMorgan/pelican,ehashman/pelican,ehashman/pelican,Summonee/pelican,joetboole/pelican,florianjacob/pelican,catdog2/pelican,garbas/pelican,51itclub/pelican,ls2uper/pelican,jimperio/pelican,gymglish/pelican,51itclub/pelican,florianjacob/pelican,douglaskastle/pelican,simonjj/pelican,zackw/pelican,lucasplus/pelican,joetboole/pelican,deved69/pelican-1,Scheirle/pelican,UdeskDeveloper/pelican,Summonee/pelican,avaris/pelican,lazycoder-ru/pelican,farseerfc/pelican,GiovanniMoretti/pelican,abrahamvarricatt/pelican,deved69/pelican-1,Summonee/pelican,lazycoder-ru/pelican,farseerfc/pelican,karlcow/pelican,karlcow/pelican,ehashman/pelican,Scheirle/pelican,UdeskDeveloper/pelican,JeremyMorgan/pelican,rbarraud/pelican,abrahamvarricatt/pelican,lucasplus/pelican,iKevinY/pelican,GiovanniMoretti/pelican,douglaskastle/pelican,gymglish/pelican,simonjj/pelican,garbas/pelican,rbarraud/pelican,Rogdham/pelican,zackw/pelican,getpelican/pelican,garbas/pelican,getpelican/pelican,deved69/pelican-1,simonjj/pelican,lucasplus/pelican,abrahamvarricatt/pelican,ls2uper/pelican,talha131/pelican,rbarraud/pelican,number5/pelican,UdeskDeveloper/pelican,51itclub/pelican,JeremyMorgan/pelican,Rogdham/pelican,jimperio/pelican,lazycoder-ru/pelican,florianjacob/pelican,GiovanniMoretti/pelican,ingwinlu/pelican,zackw/pelican,number5/pelican,iKevinY/pelican,catdog2/pelican,joetboole/pelican