ARROW-1493: [C++] Flush stream in PrettyPrint functions
ARROW-1493: [C++] Flush stream in PrettyPrint functions

I'm not sure how to test this.

Author: Wes McKinney <wes.mckinney@twosigma.com>

Closes #1066 from wesm/ARROW-1493 and squashes the following commits:

ffbb9af8 [Wes McKinney] Flush stream in PrettyPrint functions

apache/arrow,kou/arrow,laurentgo/arrow,cpcloud/arrow,dremio/arrow,kou/arrow,itaiin/arrow,wagavulin/arrow,xhochy/arrow,pcmoritz/arrow,icexelloss/arrow,itaiin/arrow,laurentgo/arrow,dremio/arrow,majetideepak/arrow,laurentgo/arrow,laurentgo/arrow,xhochy/arrow,laurentgo/arrow,wagavulin/arrow,kou/arrow,icexelloss/arrow,icexelloss/arrow,icexelloss/arrow,yufeldman/arrow,cpcloud/arrow,pcmoritz/arrow,cpcloud/arrow,xhochy/arrow,icexelloss/arrow,yufeldman/arrow,kou/arrow,xhochy/arrow,tebeka/arrow,dremio/arrow,kou/arrow,renesugar/arrow,dremio/arrow,tebeka/arrow,tebeka/arrow,renesugar/arrow,majetideepak/arrow,NonVolatileComputing/arrow,laurentgo/arrow,apache/arrow,wesm/arrow,itaiin/arrow,siddharthteotia/arrow,apache/arrow,dremio/arrow,apache/arrow,renesugar/arrow,laurentgo/arrow,tebeka/arrow,NonVolatileComputing/arrow,cpcloud/arrow,itaiin/arrow,dremio/arrow,itaiin/arrow,wesm/arrow,kou/arrow,xhochy/arrow,majetideepak/arrow,itaiin/arrow,kou/arrow,apache/arrow,siddharthteotia/arrow,icexelloss/arrow,pcmoritz/arrow,wagavulin/arrow,wesm/arrow,pcmoritz/arrow,yufeldman/arrow,icexelloss/arrow,majetideepak/arrow,tebeka/arrow,cpcloud/arrow,majetideepak/arrow,apache/arrow,renesugar/arrow,cpcloud/arrow,kou/arrow,NonVolatileComputing/arrow,majetideepak/arrow,kou/arrow,xhochy/arrow,pcmoritz/arrow,siddharthteotia/arrow,itaiin/arrow,renesugar/arrow,wesm/arrow,laurentgo/arrow,itaiin/arrow,pcmoritz/arrow,pcmoritz/arrow,pcmoritz/arrow,wagavulin/arrow,NonVolatileComputing/arrow,renesugar/arrow,wagavulin/arrow,wesm/arrow,laurentgo/arrow,cpcloud/arrow,wagavulin/arrow,renesugar/arrow,laurentgo/arrow,kou/arrow,cpcloud/arrow,majetideepak/arrow,icexelloss/arrow,tebeka/arrow,siddharthteotia/arrow,apache/arrow,cpcloud/arrow,yufeldman/arrow,kou/arrow,wagavulin/arrow,siddharthteotia/arrow,icexelloss/arrow,dremio/arrow,itaiin/arrow,kou/arrow,siddharthteotia/arrow,renesugar/arrow,xhochy/arrow,NonVolatileComputing/arrow,yufeldman/arrow,siddharthteotia/arrow,xhochy/arrow,majetideepak/arrow,NonVolatileComputing/arrow,xhochy/arrow,yufeldman/arrow,xhochy/arrow,wesm/arrow,majetideepak/arrow,cpcloud/arrow,cpcloud/arrow,cpcloud/arrow,wesm/arrow,NonVolatileComputing/arrow,icexelloss/arrow,wagavulin/arrow,itaiin/arrow,yufeldman/arrow,xhochy/arrow,NonVolatileComputing/arrow,NonVolatileComputing/arrow,apache/arrow,laurentgo/arrow,majetideepak/arrow,icexelloss/arrow,renesugar/arrow,xhochy/arrow,dremio/arrow,renesugar/arrow,wesm/arrow,tebeka/arrow,majetideepak/arrow,yufeldman/arrow,apache/arrow,laurentgo/arrow,wagavulin/arrow,dremio/arrow,cpcloud/arrow,siddharthteotia/arrow,icexelloss/arrow,tebeka/arrow,icexelloss/arrow,pcmoritz/arrow,wagavulin/arrow,renesugar/arrow,laurentgo/arrow,dremio/arrow,wesm/arrow,apache/arrow,renesugar/arrow,xhochy/arrow,renesugar/arrow,wesm/arrow,pcmoritz/arrow,siddharthteotia/arrow,wesm/arrow,apache/arrow,majetideepak/arrow,pcmoritz/arrow,wesm/arrow,pcmoritz/arrow,kou/arrow,wesm/arrow,cpcloud/arrow,icexelloss/arrow,tebeka/arrow,wesm/arrow,itaiin/arrow,majetideepak/arrow,wagavulin/arrow,itaiin/arrow,pcmoritz/arrow,pcmoritz/arrow,siddharthteotia/arrow,NonVolatileComputing/arrow,kou/arrow,yufeldman/arrow,xhochy/arrow,majetideepak/arrow,itaiin/arrow,apache/arrow,apache/arrow,majetideepak/arrow,tebeka/arrow,yufeldman/arrow,apache/arrow,renesugar/arrow,xhochy/arrow,siddharthteotia/arrow,itaiin/arrow,laurentgo/arrow,pcmoritz/arrow,laurentgo/arrow,dremio/arrow,NonVolatileComputing/arrow,renesugar/arrow,itaiin/arrow,wagavulin/arrow,yufeldman/arrow