Repository: conda/conda

Issue:
unsatisfiability crashes conda canary 4.2.5, rather than giving error output 
I have a python 3 environment, with the lastest conda in conda-canary, that is

```
Current conda install:

               platform : linux-64
          conda version : 4.2.5
       conda is private : False
      conda-env version : 2.6.0
    conda-build version : 1.19.2
         python version : 2.7.12.final.0
       requests version : 2.10.0
```

If I try to install something that won't fit, for instance

```
conda install MySQL-python
```

then I get

```
Traceback (most recent call last):
  File "/reg/g/psdm/sw/conda/inst/miniconda2-dev-rhel7/lib/python2.7/site-packages/conda/exceptions.py", line 471, in conda_exception_handler
    return_value = func(*args, **kwargs)
  File "/reg/g/psdm/sw/conda/inst/miniconda2-dev-rhel7/lib/python2.7/site-packages/conda/cli/main.py", line 144, in _main
    exit_code = args.func(args, p)
  File "/reg/g/psdm/sw/conda/inst/miniconda2-dev-rhel7/lib/python2.7/site-packages/conda/cli/main_install.py", line 80, in execute
    install(args, parser, 'install')
  File "/reg/g/psdm/sw/conda/inst/miniconda2-dev-rhel7/lib/python2.7/site-packages/conda/cli/install.py", line 370, in install
    raise CondaError('UnsatisfiableSpecifications', e)
TypeError: __init__() takes exactly 2 arguments (3 given)
```

unsatisfiability crashes conda canary 4.2.5, rather than giving error output 
I have a python 3 environment, with the lastest conda in conda-canary, that is

```
Current conda install:

               platform : linux-64
          conda version : 4.2.5
       conda is private : False
      conda-env version : 2.6.0
    conda-build version : 1.19.2
         python version : 2.7.12.final.0
       requests version : 2.10.0
```

If I try to install something that won't fit, for instance

```
conda install MySQL-python
```

then I get

```
Traceback (most recent call last):
  File "/reg/g/psdm/sw/conda/inst/miniconda2-dev-rhel7/lib/python2.7/site-packages/conda/exceptions.py", line 471, in conda_exception_handler
    return_value = func(*args, **kwargs)
  File "/reg/g/psdm/sw/conda/inst/miniconda2-dev-rhel7/lib/python2.7/site-packages/conda/cli/main.py", line 144, in _main
    exit_code = args.func(args, p)
  File "/reg/g/psdm/sw/conda/inst/miniconda2-dev-rhel7/lib/python2.7/site-packages/conda/cli/main_install.py", line 80, in execute
    install(args, parser, 'install')
  File "/reg/g/psdm/sw/conda/inst/miniconda2-dev-rhel7/lib/python2.7/site-packages/conda/cli/install.py", line 370, in install
    raise CondaError('UnsatisfiableSpecifications', e)
TypeError: __init__() takes exactly 2 arguments (3 given)
```



Discussion:

Resolving patch:
diff --git a/conda/cli/install.py b/conda/cli/install.py
--- a/conda/cli/install.py
+++ b/conda/cli/install.py
@@ -15,7 +15,7 @@
 from difflib import get_close_matches
 from os.path import abspath, basename, exists, isdir, join
 
-from .. import CondaError, text_type
+from .. import text_type
 from .._vendor.auxlib.ish import dals
 from ..api import get_index
 from ..base.constants import ROOT_ENV_NAME
@@ -367,7 +367,7 @@ def install(args, parser, command='install'):
         # Unsatisfiable package specifications/no such revision/import error
         if e.args and 'could not import' in e.args[0]:
             raise CondaImportError(text_type(e))
-        raise CondaError('UnsatisfiableSpecifications', e)
+        raise
 
     if nothing_to_do(actions) and not newenv:
         from .main_list import print_packages


Test patch: