Delete wheels before attempting source upload

If wheels are present in the dist/ directory, the pypi deploy mechamism
will try to upload these as well as the source distribution, which then
fails because the name already exists on pypi.

To make the source/binary distinction more robust and elegant, use -z
and if [[ $VAR ]] checks to figure distinguish source and binary
deploys.

.travis.yml

@@ -110,12 +110,19 @@ script:
 before_deploy:
   # OS X ships with a tar that doesn't support --exclude-vcs, which is
   # unproblematic as long as source code is uploaded from linux.
+  #
+  # when doing source deploy, remove the dist directory with pre-built wheels,
+  # otherwise they get picked up instead, which will surely fail because the
+  # wheel has already been uploaded to pypi.
   - if [[ "$TRAVIS_OS_NAME" == "linux" && ! -d segyio-$VERSION ]]; then
       git clone $TRAVIS_BUILD_DIR segyio-$VERSION;
       echo "version = '$TRAVIS_TAG'" > segyio-$VERSION/python/segyio/version.py;
       tar --exclude-vcs -C $TRAVIS_BUILD_DIR -czvf segyio-$VERSION.tar.gz segyio-$VERSION;
       zip --exclude *.git -r segyio-$VERSION.zip $TRAVIS_BUILD_DIR/segyio-$VERSION/*;
     fi
+  - if [[ $SOURCEDEPLOY ]]; then
+      rm -rf dist;
+    fi
 
 deploy:
     - provider: pypi # source distribution (done from linux python 3.6 only)
@@ -125,7 +132,7 @@ deploy:
       password:
         secure: WHeA5x2iiXzjYXdgZeJU6l4fawRi/umqH1713QAj0RPZBAnD+9m8Zrpn2UWn9+1dtx6xUMkNg3ZTueVKTKo0f2i/4o0xkzQ5BW11cetCWusV2Dku1btPTA5Fhs+dvPDlL3m496a3Bq/A/fRDj5JLDiiPibvpM01lEBxFKYooWGQ75HVuhnAt57vabD45gDpIE7N23+So4+9bsG/nT/ZlgoaS01uLTdlnf6tjNgP0/UBkonmedC62iVvCu7itfHZMTY2rSeww7KBMI3s7Gz+cyx9IbI3shbDpdJGHpM8Qe+1oFi31Z+DylWQA5SkpHlLMUP+zjMKLF+1hXGNUeJuyadIFrxzbS3vTV2yRPa6ol8q+bX7YLy0xNLSE8aMm54LKgXfRKLc3G8d3I33oEfyk5hygY8iEX728r2TsARslYxOF3sZqJvY8lx4GBEDiXxX2GJvGCPy/Uby786uWnZlFFkDERk3nawE0W68zY0GElbutq6HMSk6v49J7em9Rg/QLptjoa0uF2A9Cy+BAJcnfauIawOG3UPXZ8kD60PTbu8tqtwtXO5lzTSIOr1lt3+6R8GmCc2hz2YXELKvdnZWYCXAjnNuC4eESlp7zxmzhpOVkb2Jy1v6rGKpcxVMggLQbOjOGWPLg9q4+OZQBw5bhMGmVGQhSBuxzEb/wBRy9XV8=
       on:
-        condition: $SOURCEDEPLOY == 1
+        condition: $SOURCEDEPLOY
         tags: true
 
     - provider: pypi # upload built wheels
@@ -136,7 +143,7 @@ deploy:
       password:
         secure: 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
       on:
-        condition: $SOURCEDEPLOY != 1
+        condition: -z $SOURCEDEPLOY
         tags: true
 
     - provider: releases # upload tarball and zip with source code
@@ -149,4 +156,4 @@ deploy:
         secure: 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
       on:
         tags: true
-        condition: $SOURCEDEPLOY == 1
+        condition: $SOURCEDEPLOY