REQ: failover mpfr.org to mirror in build scripts

[madeinoz67]

There appears to be reliability issues with www.mpfr.org and so far today Its been down after trying to do a new install.

After doing a bit of googling it would seem that this is a fairly common thing, also other OS projects that use www.mpfr.org also have ongoing intermittent reliability issues from the results of posts Ive read in their forums etc .

Is it possibly to include in the build scripts the ability to failover to a mirror site to get necessary toolchain components if the connection fail?

[pfalcon]

See #100 . Also, #146 may or may not alleviate this problem. Feel free to test and report.