FIX inconsistent error on push for existing paper.

The error raised by Repository.push_paper was different depending on
whether the existence of the paper in the repository was tested directly
through the filebroker (quicker when list of citekeys in not loaded) or
through the regular __contains__ method.

pubs/filebroker.py

@@ -71,12 +71,12 @@ class FileBroker(object):
             os.remove(bibfilepath)
 
     def exists(self, citekey, both=True):
+        meta_exists = check_file(os.path.join(self.metadir, citekey + '.yaml'), fail=False)
+        bib_exists = check_file(os.path.join(self.bibdir, citekey + '.bib'), fail=False)
         if both:
-            return (check_file(os.path.join(self.metadir, citekey + '.yaml'), fail=False) and
+            return meta_exists and bib_exists
-                    check_file(os.path.join(self.bibdir, citekey + '.bib'), fail=False))
         else:
-            return (check_file(os.path.join(self.metadir, citekey + '.yaml'), fail=False) or
+            return meta_exists or bib_exists
-                    check_file(os.path.join(self.bibdir, citekey + '.bib'), fail=False))
 
 
     def listing(self, filestats=True):

pubs/repo.py

@@ -1,5 +1,3 @@
-import shutil
-import glob
 import itertools
 
 from . import bibstruct
@@ -7,6 +5,7 @@ from . import events
 from . import datacache
 from .paper import Paper
 
+
 def _base27(n):
     return _base27((n - 1) // 26) + chr(ord('a') + ((n - 1) % 26)) if n else ''
 
@@ -65,9 +64,8 @@ class Repository(object):
                                if True, mimick the behavior of updating a paper
         """
         bibstruct.check_citekey(paper.citekey)
-        if (not overwrite) and self.databroker.exists(paper.citekey, both = False):
+        if (not overwrite) and (self.databroker.exists(paper.citekey, both=False)
-            raise IOError('files using the {} citekey already exists'.format(paper.citekey))
+                                or (citekey in self)):
-        if (not overwrite) and self.citekeys is not None and paper.citekey in self.citekeys:
             raise CiteKeyCollision('citekey {} already in use'.format(paper.citekey))
 
         self.databroker.push_bibdata(paper.citekey, paper.bibdata)
@@ -138,4 +136,3 @@ class Repository(object):
         for p in self.all_papers():
             tags = tags.union(p.tags)
         return tags
-