Add a top-level gitignore file with various things we don't want checked in by mistake. Re #3977.

.gitignore

+# Took these from the https://github.com/github/gitignore project on October 21, 2011
+
+# Ignore text editor (e.g. emacs) autosave files
+*~
+
+# Ignore CMake generated files (if someone does an in-source build)
+CMakeCache.txt
+CMakeFiles
+Makefile
+cmake_install.cmake
+install_manifest.txt
+
+# Compiled Object files
+*.slo
+*.lo
+*.o
+
+# Compiled Dynamic libraries
+*.so
+
+# Compiled Static libraries
+*.lai
+*.la
+*.a
+
+# Compiled python files
+*.py[co]
+
+# Eclipse-generated files
+*.pydevproject
+.project
+.metadata
+bin/**
+tmp/**
+tmp/**/*
+*.tmp
+*.bak
+*.swp
+*~.nib
+local.properties
+.classpath
+.settings/
+.loadpath
+
+# External tool builders
+.externalToolBuilders/
+
+# Locally stored "Eclipse launch configurations"
+*.launch
+
+# CDT-specific
+.cproject
+
+# PDT-specific
+.buildpath
+
+## Ignore Visual Studio temporary files, build results, and
+## files generated by popular Visual Studio add-ons.
+
+# User-specific files
+*.suo
+*.user
+*.sln.docstates
+
+# Build results
+[Dd]ebug/
+[Rr]elease/
+*_i.c
+*_p.c
+*.ilk
+*.meta
+*.obj
+*.pch
+*.pdb
+*.pgc
+*.pgd
+*.rsp
+*.sbr
+*.tlb
+*.tli
+*.tlh
+*.tmp
+*.vspscc
+.builds
+
+# Visual C++ cache files
+ipch/
+*.aps
+*.ncb
+*.opensdf
+*.sdf
+
+# Visual Studio profiler
+*.psess
+*.vsp
+
+# ReSharper is a .NET coding add-in
+_ReSharper*
+
+# Installshield output folder
+[Ee]xpress
+
+# DocProject is a documentation generator add-in
+DocProject/buildhelp/
+DocProject/Help/*.HxT
+DocProject/Help/*.HxC
+DocProject/Help/*.hhc
+DocProject/Help/*.hhk
+DocProject/Help/*.hhp
+DocProject/Help/Html2
+DocProject/Help/html
+
+# Click-Once directory
+publish
+
+# Others
+[Bb]in
+[Oo]bj
+sql
+TestResults
+*.Cache
+ClientBin
+stylecop.*
+~$*
+*.dbmdl
+Generated_Code #added for RIA/Silverlight projects
+
+# Backup & report files from converting an old project file to a newer
+# Visual Studio version. Backup files are not needed, because we have git ;-)
+_UpgradeReport_Files/
+Backup*/
+UpgradeLog*.XML
+
+# Subversion directories
+.svn/
+
+# Windows image file caches
+Thumbs.db
+
+# Folder config file
+Desktop.ini
+