csvstat chokes on "inf" numbers
For the following input CSV (yes, 1 row, 1 column, 1 header):

    headerA
    inf

`csvstat` (no other argument besides input.csv) outputs:

```
  1. "columnA"

	Type of data:          Number
	Contains null values:  False
	Unique values:         1
	Most common values:    [<class 'decimal.InvalidOperation'>]
```

This happens because `python-babel` (in Debian system 2.4.0) number formatting function chokes on Infinity, e.g.:
```
from decimal import Decimal
from babel.numbers import format_decimal
format_decimal(Decimal("Infinity"))
```

`format_decimal` is called from `csvstat.py:269` (in Debian system 1.0.2-1).

Interestingly `csvstat --freq` outputs:
```
{ "Infinity": 1 }
```

diff --git a/csvkit/utilities/csvstat.py b/csvkit/utilities/csvstat.py
index 9aecdc9..fb1ecb2 100644
--- a/csvkit/utilities/csvstat.py
+++ b/csvkit/utilities/csvstat.py
@@ -190,7 +190,7 @@ class CSVStat(CSVKitUtility):
                     op = OPERATIONS[op_name]['aggregation']
                     stat = table.aggregate(op(column_id))
 
-                    if isinstance(stat, Decimal):
+                    if isinstance(stat, Decimal) and stat.is_finite():
                         stat = format_decimal(stat, locale=agate.config.get_option('default_locale'))
             except:
                 stat = None
@@ -224,7 +224,7 @@ class CSVStat(CSVKitUtility):
                         op = op_data['aggregation']
                         v = table.aggregate(op(column_id))
 
-                        if isinstance(v, Decimal):
+                        if isinstance(v, Decimal) and v.is_finite():
                             v = format_decimal(v, locale=agate.config.get_option('default_locale'))
 
                         stats[op_name] = v
@@ -268,7 +268,7 @@ class CSVStat(CSVKitUtility):
                         if isinstance(column.data_type, agate.Number):
                             v = row[column_name]
 
-                            if isinstance(v, Decimal):
+                            if isinstance(v, Decimal) and v.is_finite():
                                 v = format_decimal(v, locale=agate.config.get_option('default_locale'))
                         else:
                             v = six.text_type(row[column_name])
['csvkit/utilities/csvstat.py']